As far as the valve covers go...Assuming it has a 3.0 engine which i believe was the only engine available at that time in pathy's...they are a challenge for the average mechanic. But can be done with a few hours and a lot of patience. as for the rear pinion seal and transfer case they are probably not that bad but appear bad due to the valve covers leaking down onto everything. I would change the valve cover gaskets first and clean the engine compartment. Then drive it for a little while and recheck for other leaks.