It sounds like you have a 1955 or later transmission, correct? It doesn't matter, really; the torque converter should drain pretty quickly after shutting off the engine, which means the fluid level should rise above the normal full mark (running, hot level). I don't remember specifically, but I'm sure there is a seal on the shifter shaft, although I think it is only accessible from inside the case. There is another shaft for the throttle valve, which has the throttle rod that attaches to the carburetor. That shaft also has a seal, I'm sure, but again I don't remember specifically. The throttle valve is inside a squarish cover at the base of the torque converter housing. There should be a shaft extending from the cover; the shaft should have a lever attached, which in turn holds the throttle rod that attaches to the carburetor. That whole mechanism gives the kick-down (passing gear) when you go to wide-open throttle.
Another possibility for the rear seal leakage is a groove on the seal surface of the U-joint yoke. Did you check that?
Don't know if this answers your question, but maybe it will help.
Harvester
