When I bought the Z it had a 5 speed that would pop out of 5th and not go into reverse so I swapped in a dogleg 5 speed out of a 280zx. The transmission had low miles and was in great shape I cleaned it up and threw it in. I swapped speedometer gears to one that would fit for my car. Until today I could not figure out how or why i keep getting a slow but steady transmission oil leak. Apparently its a common problem. Today I found the solution thanks to the nicoclub.com.
In my situation, I made sure that the outer rubber seal was replaced with one in good condition. I didn’t even think to look for one where the speed gear went. Its always the little things..
Updates on this when I get a chance to work on the Z.