Mine is a 2000 too and it has a leaky rear main. It has not really gotten better or worse. It drips a couple drops each night, but that is it. Unlike your XJ the TJ has a two piece rear main seal, but not on all years. Someone will have to chime in on your year. The parts to fix the two piece rear mains seal are only like $30.
2000 Sahara, 3.5" Rubicon Express Lift, 1" spring spacer & 1" Body Lift, 35" BFG Mud tires, Front & Rear ARB, Rancho 9000 shocks, UCF Ultra High Belly Up