904 Leaking. What to check first?

The trick is getting clearance to operate the tool from above.

I put a bottle jack under the tailshaft, dropped the crossmember and let the tailshaft drop down slowly to get some extra clearance to work. I've seen some cut a hole in the floor and get it from inside the cab.

I pulled the pan and used a socket, washers and some threaded rod to press the seal in.