I have used 1-shot grease for years on my 109- When I finally did replace the swivel seals, the innards were in great shape.
If your oil leak has gotten into the brakes, it's not a swivel seal that's gone but a hub seal. This is a rubber seal that sits inside the inner side of the hub, immediately inboard of the inner wheel bearings, preventing oil leaking from the svivel housing and hub assy into the brake assy.
To replace it, you need to remove the wheel, drive flange, outer wheel bearings and hub. Check the stub axles for wear on the seal face and bearing locations. Any wear on this also means replacement (expensive).
While you're replacing the seal, I'd replace the bearings too. The Gen Parts kit costs £15 and has both brgs, hub seal, drive flange gasket, hub nut lock washer (the big one), hub cap and o-ring.
If the shoes have been contaminated, replace them too and clean the drums carefully.
While you're doing all this, you can also bleed the front brakes (109 dual line) perfectly by removing the backplate from the swivel housing, and bleeding with the plate held horizontally with pipe work upwards. Refit the brakes, followed by the hub, and at the end you'll notice significantly sharper brakes. Aloow a day to complete both sides at a leisurely pace.