Bfg

I have a transmission leak and it seems to be leaking from the manual shaft seal. Has anyone replaced this seal? I have a service manual but want to know how difficult this job is? Thank you.

65vistacruiser

Simple, with the right tool. There is a lever seal extractor and installation tool from KD tool which makes it very easy. You don't even need to drop the pan.
Just to be clear, if you're careful it can be done without the tool, with the shaft in place and you need not drop the pan. But prying out the seal you could mar the shaft and have it still leak.

If you want to change the ATF anyway, you could just do this, drop the pan, remove the lever shaft from the trans and pry out the old seal. A 9/16 open end wrench is needed to unscrew the inside nut on the rooster comb. Look at the inside linkage "s" hook and make sure you install it correctly. The TH350 has a spring-clip on the inner shaft which maintains the position of the rooster comb inside the trans, with out it the "s" hook will fall out. The clip can simply be pried off using a screwdriver or a hook shaped tool. To re-install the clip, I lay the clip into the yoke of a 3/4 open end wrench, and push it back onto the shaft, after the S hook is in place.
You can drive the new seal in using a socket and hammer, make sure it goes in strait and un-damaged.

There are long and short versions of the tool. Short will work on a TH350/400 and early 700r4, long is required on a later 4L60E or 4L80E and should work on the 350 as well.
https://www.google.com/search?q=leve...uPUyW3TXMlI%3D