Hey gang, I have been away for a very long time. Went through a painful divorce so the Vette had to sit for quite a while. Anyway, all is good now (as good as it can be!) I rebuilt my 4 spd last year and was all happy with the results until the morning after the test run left tranny grease all over the garage floor. I finally got to pulled the tranny back out last weekend expecting the leak to be the front seal and to my surprise the leak is coming from the countershaft.

Th e front of the case, where the countershaft goes thru, is simply a press fit...no seal. What you need to do is clean it off very well, and seal around the shaft hole with sillycone, then smooth it out. Assemble the trans back in the car as soon as you can after putting the sealer on it, so it doesn't harden, and not allow the trans to set flush on the bell housing.
This is a common issue with the Muncies, and the BW T10 designs. I always just cover the area with sillycone when I build them. The problem is solved.

Awesome! I was hoping that would be the answer. Have a good one.

You can also put some lock tite on the end while you are building the transmission before you set it in place.