68, m20 is leaking at the tail shaft.
I see Rockauto has a few bushing and seal kits listed,
Which one is the way to go? Are they all the same?

 

Skip rock auto and call Autogear in Syracuse, Ny. They will get you the right parts.

 

I’m not a 4 speed guy, but I’m pretty sure you have to options for seals and bushings. It’s either the smaller 27 spline used on later model Powerglides, th350, 700 and 2004R, or the bigger 32 spline for the TH400 and the larger output shaft manual transmission.