I've been dealing with dangerously vague steering on my '03 for the better part of the past year. After adjusting (and then replacing) the gearbox didn't settle it, I bit the bullet and final decided to go through the track rod, drag link, and ball joint replacement.
I'd been putting it off thinking that it would be a gigantic nightmare, but in the end it was one of the easier jobs that I had undertaken on my Disco - no more difficult than working on a tractor. In fact I'd rate plug/wire/coil replacements at a higher difficulty than this job.
I was an idiot to have waited this long, and I really think anyone that has iffy steering should look into doing this - there is nothing about it that a driveway mechanic can't do. Air tools certainly helped, but just in terms of speed - every bolt is easily accessible and if you have a decent set of hand tools and a couple of big hammers, you're good to go. The ball joint press rents from Advance for free and has all the fittings we need.
I'll do a write-up if there are any interested parties, but the gist of it is.
1. Place truck on jackstands, remove wheels.
2. Unbolt steering damper, remove track rod and drag link. (4 nuts, 1 bolt)
3. Undo caliper bracket bolts and remove caliper. (2 bolts/side)
4. Remove rotor and dust shield. (1 screw, 3 bolts)
5. Undo ABS sensor bolt. (1 socket cap bolt)
6. Undo hub bolts (4 bolts)
7. Separate hub from knuckle, remove with half-shaft attached.
8. Undo top and bottom ball joint nuts (2 nuts)
9. Using pickle fork and hammer, separate knuckle from ball joints.
10. Using press, remove top, then bottom ball joints.
Reassembly is the reverse.
After about 2 hours of work I got to this point:

Both dust boots were completely shot, and while the top joint was still usable, the bottom joint was so utterly destroyed. There was no resistance in it at all, and there was tons (1-2mm) of free play in the up/down and side/side axis. This explains my dead steering and clunking over bumps.
After a few more hours:

New units are in. I opted with the Lemforder units available from Miami British for $115/4. Yes, you can find cheaper kits, but only $30 or so cheaper, and you really don't want to skimp. Chinese bearings of any sort notorious for low grease quality, low metal quality, and bad tolerances. The new joints were made in the UK, use a high quality moly grease, and high quality silicone boots. Measurements were taken with a caliper and they were pretty much identical to the OEM measurements. They fit perfectly and went in without a problem. They don't feature grease nipples but I figure if I got 115K miles out of the old ones this should be a one-time job.
This is where air tools help:

RAVE calls for the removal of the axle stake nuts when pulling the hub, but it is only necessary if you are servicing the hub. Otherwise, the hub/shaft assembly will pull out of the axle in one piece - just remember to replace the oil seals when you're doing the reassembly. I wanted to pull my hubs anyway to check for play and replace a stud, so I did the removal. Left side was a breeze, right side would not budge. I used PB blaster, 400ft/lb air impact, 4ft breaker bar, torch, and couldn't get it to move. Eventually I broke down and used a rotary tool. Fortunately the nuts are made of soft steel and cut quickly.
Replacement track rod/drag link.

Terrafirma heavy duty set - available from Miami British for $255. Yes, they are COMPLETE overkill (they weigh probably 3 times as much as OEM), but it is in fact CHEAPER to buy this than the OEM versions. Furthermore, it comes with 4 nuts and the tie rod ends have grease nipples. No-brainer I think.
Like I said, I'll follow up with a more photo-heavy DIY, but for now I just want people to realize that it's pretty simple to do this job and the results are outstanding. It makes the truck handle better, the suspension is quieter, and it's just so much more pleasant to drive.
If you guys have any questions, feel free to ask.
I'd been putting it off thinking that it would be a gigantic nightmare, but in the end it was one of the easier jobs that I had undertaken on my Disco - no more difficult than working on a tractor. In fact I'd rate plug/wire/coil replacements at a higher difficulty than this job.
I was an idiot to have waited this long, and I really think anyone that has iffy steering should look into doing this - there is nothing about it that a driveway mechanic can't do. Air tools certainly helped, but just in terms of speed - every bolt is easily accessible and if you have a decent set of hand tools and a couple of big hammers, you're good to go. The ball joint press rents from Advance for free and has all the fittings we need.
I'll do a write-up if there are any interested parties, but the gist of it is.
1. Place truck on jackstands, remove wheels.
2. Unbolt steering damper, remove track rod and drag link. (4 nuts, 1 bolt)
3. Undo caliper bracket bolts and remove caliper. (2 bolts/side)
4. Remove rotor and dust shield. (1 screw, 3 bolts)
5. Undo ABS sensor bolt. (1 socket cap bolt)
6. Undo hub bolts (4 bolts)
7. Separate hub from knuckle, remove with half-shaft attached.
8. Undo top and bottom ball joint nuts (2 nuts)
9. Using pickle fork and hammer, separate knuckle from ball joints.
10. Using press, remove top, then bottom ball joints.
Reassembly is the reverse.
After about 2 hours of work I got to this point:

Both dust boots were completely shot, and while the top joint was still usable, the bottom joint was so utterly destroyed. There was no resistance in it at all, and there was tons (1-2mm) of free play in the up/down and side/side axis. This explains my dead steering and clunking over bumps.
After a few more hours:

New units are in. I opted with the Lemforder units available from Miami British for $115/4. Yes, you can find cheaper kits, but only $30 or so cheaper, and you really don't want to skimp. Chinese bearings of any sort notorious for low grease quality, low metal quality, and bad tolerances. The new joints were made in the UK, use a high quality moly grease, and high quality silicone boots. Measurements were taken with a caliper and they were pretty much identical to the OEM measurements. They fit perfectly and went in without a problem. They don't feature grease nipples but I figure if I got 115K miles out of the old ones this should be a one-time job.
This is where air tools help:

RAVE calls for the removal of the axle stake nuts when pulling the hub, but it is only necessary if you are servicing the hub. Otherwise, the hub/shaft assembly will pull out of the axle in one piece - just remember to replace the oil seals when you're doing the reassembly. I wanted to pull my hubs anyway to check for play and replace a stud, so I did the removal. Left side was a breeze, right side would not budge. I used PB blaster, 400ft/lb air impact, 4ft breaker bar, torch, and couldn't get it to move. Eventually I broke down and used a rotary tool. Fortunately the nuts are made of soft steel and cut quickly.
Replacement track rod/drag link.

Terrafirma heavy duty set - available from Miami British for $255. Yes, they are COMPLETE overkill (they weigh probably 3 times as much as OEM), but it is in fact CHEAPER to buy this than the OEM versions. Furthermore, it comes with 4 nuts and the tie rod ends have grease nipples. No-brainer I think.
Like I said, I'll follow up with a more photo-heavy DIY, but for now I just want people to realize that it's pretty simple to do this job and the results are outstanding. It makes the truck handle better, the suspension is quieter, and it's just so much more pleasant to drive.
If you guys have any questions, feel free to ask.