Welcome. The whole factory manual set, called the RAVE, is a free download below. Also see
Major Service. for service items to catch up, and check out our tech area, in particular a write up on how to refit the front drive shaft with grease fittings. The stock shaft will chirp, split, and spear a hole in the transmission, usually well over $5,000 repair bill. If changing thermostat consider flush of radiator and change to green coolant, especially if fitted with orange Dexcool. This time of year you can run 15W40 Rotella or if really cold, 5W40 Rotella (by Shell). It is a diesel rated oil that has a lot of cleaning chemicals well suited for the older design engines. 10W30 is too light. You should also look at transmission flush, filter, and new fluid; and diffs and transfer case. Lots of things on the bottom side of a Disco. On the serious PM side, consider a manual oil pressure test, so you will know if your oil pump is up to spec.