Best bet is to change it yourself. The dealer is just trying to scare you. Nothing magical about changing oil on a Disco. All you need to do is:
1. Order up a filter from RoversNorth, or wherever.
2. Unscrew drainplug & drain the oil into one of those large aluminum foil caserole dishes you can get for a buck or two at the grocery store.
3. Replace old filter with new (expect some dripping). Screw the drain plug back in (important step
) You can hand-tighten the new filter,,that wrench-thingy is not necessary.
4. Pour in new oil,,,should take 5-6 quarts
5. Using a cheap plastic funnel, pour the old oil from caserole dish back into the now-empty containers from your new oil.
6. Take the old oil to a Jiffy Lube or wherever,,,they will charge you a very small disposal fee.
Total cost to you is about: $2.00 for foil caserole dish,,, @$2-3.00 per quart of oil retail,,, @$1.00 for the plastic funnel (which you can reuse over & over),,, @$20-ish for the filter depending on brand. A few bucks for disposal fee.