I don't think just priming the engine will check for a rear seal leak.
I believe you need rotational force of the crank, and crank case pressure to truly see if it leaks.
I.E. engine running.
Well I didn't see any leaks but we have it in the car and are just finishing up the exhaust and other miscellaneous connections. We should have ot running in a couple of hours, stay tuned.
