If it is leaking really badly still Kyle, then pull the trans and then the bellhousing, and replace the rear seal. Otherwise wait until you do a clutch job. The front seal is easy, and to tell the truth I would just slip another felt one in there unless you need to go further into the engine to do gears or a cam. You have enough time into this job now.
Some of the later B20s had just the neoprene seal on the rear, and felt on the front. If you know you have felt on each end, just get one of each. Soak the new one in oil, remove the big circlip and the plate, and carefully stuff the new felt into place. Install the plate and circlip and be SURE the clip engages the groove. That's it. When new, with a good crankcase breather, the felt seals work well for many miles. Mostly they leak after a rebuild if the builder does not properly center the housing to the crankshaft. About .003 variation radially is all they will tolerate. But there is a trick....as usual.
You are just going to replace the felt, so its not a problem.
I think there is another "o" in automotion in you signature by the way.
I am glad to hear the used engine is working so well.
Rhys