tanny problem

I am going to buy my friends 510 with a 85 300zx and its is leaking tranny fluid right from where the driveline goes into the tranny and the driveline wiggles a tad bit back in forth and we were thinking the leaking could be from the input/output seal and the wiggling from bad u-joints anyone know of anything else it could be i would greatly apperciate the help so i could get it running at 100 percent