REAR MAIN SEAL

99 cherokee sport automatic trans...I'm in the middle of replacing my 4.0 with another one. I want to replace the rear main seal while the new engine is out and I want to know do I have to take off the oil pan to replace the rear main seal or can I do it with it on?

oil pan comes off

x2. no gettin around it.

Yes, it's a 2-piece seal. Oil pan and the rearmost bearing cap comes off. Good thinking to do it while the engine it out as the hardest part seems to be getting the pan off.