On any engine I've worked on, you don't necessarily have to remove the crank all the way to replace the rear seal, but it's basically the same amount of work.
Unless you can get the pan out (unlikely in most RWD vehicles) with the engine in place, you're yanking the motor.
Technically, you only have to get the main caps loose and the rear cap off to replace the rear seal, since doing so will allow you to pry the rear of the crank just enough to do the replacement. The weight of the crank might just be enough to have it give you the slack you need.
If it were me, I might be tempted to tear out the old seal any way I could, after removing only the tranny and flywheel, and very carefully tap a new one in. It's how we replace seals in motorcycle forks. Destroy the old one taking it out, and drive a new one in. But seal-drivers are readily available that put the new seals in quickly and without any risk of damaging them. I've never seen one large enough for a car's rear main seal. And wouldn't swear it's not locked into a groove in the journal anyway. If memory serves, I don't think I've ever encountered a rear seal that was any more than a press fit.
But if you find that you can't replace the seal this way, no harm done because you're yanking or at least unmounting/raising the engine anyway.
If you attempt the easy way, the most important thing is to make sure you don't turn the crank at all once you've loosened the mains, as one or more of the bearings may've stuck to the crank instead of staying put in the crankcase, and you could have a real mess if it gets out of place. If at all possible (assuming you're trying the in-car replacement and have loosened the mains to make it easier or get around a locking-groove or too-tight fit problem), make real certain all bearings are where they belong when you retighten the main caps. You'll know pretty quickly if one is out of place because light torque on the nuts or bolts won't close up the gap between the cap and the crankcase. More than 99% of the time, the bearings will stay where they belong, but don't thumb your nose at Murphy.
AI
