Well since this thread is all over the place but we are all having fun, I have some general questions as I think about attacking my leak. As I understand it, for a manual the transmission is essentially a sealed box and the transmission fluid just sloshes around in there keeping things lubricated. Obviously there's the fill hole and drain hole, plus the shaft entering and exiting the metal casing. These would be the primary points of any leak of transmission fluid. The transmission seals mentioned earlier in this thread are for the input/output shafts.
When I bought the transmission, the seller on here told me the following:
Brought it to La Jolla Independent, we put in manual transmission lubricant in and then drained it. Went through all gears and it shifts fine. Put it hot wash tank to clean it.
This test would suggest that there wasn't at least a massive obvious failing of these seals when the transmission was filled, although much like the coolant system I'd suspect that some of these leaks may not be apparent until the system is put under stress. So if/when I end up pulling the transmission, changing out front and rear transmission seals would be my primary route forward
With regards to the oil potential, the engine wasn't leaking before I removed the old 4-speed. None of the work changing clutch, bell housing, etc should have had an effect on any oil leak potential, since these areas aren't in direct contact with the engine internals, but I did change the front and rear main seals since it was one of those "while you are there" items. I don't see a leak from the front of the engine, and I did check the oil sender area - no leak there. So the likely culprit in the event of an oil leak would be the rear main seal.
Am I understanding this all correctly? Of course the real answer will be lifting the car and doing a little hunting, but I'd like to make sure that I have things conceptually down before I start undoing bolts.