Replacing rear seal w/engine in car?

Well, to change the gasket or seal for the sake of changing it , if it was not the source of the leak, is to risk the introduction of a leak. So if you do end up finding a leak there then be sure to retest after replacing parts.
The neoprene seal is easy to replace, I've done it in situ, several times. The rope seals are only a bit more difficult. I would gladly rather change it, in situ, than to pull the engine. Even without a hoist. And I have a milodon roadrace pan. And I'm 62 yrs young. And 210lbs. Piece of cake. 3M weatherstrip glue and RTV,shazzam. And if the tranny is out, double shazzam.