I have a 00 XJ with 84,000 miles on her. Runs great, no problems with performance. My question is, at what interval are you required to change the timing chain and gears. If its due, do I have to remove the oil pan to remove the cover, and be able to reseal it.

Changing the timing chain is not a regularly scheduled item. A lot of the rice burners have a timing belt and it has to be changed around 100k.