I started my engine up several weekends ago. It is mounted in the subframe and the tranny is attached. I can check for leaks real good like this and what do you know, I found one. 1 week after I started the engine/tranny combo I noticed some fresh 90 wt under the M-20, very light layer on the underbelly. Where does this come from? How could this be? The tranny is freshly rebuilt and the only thing I could come up with is the filler plug could have used a couple more turns to get it real tight.
Anyone have a similar leak?
Louie

You could put some teflon sealer (any local hardware/plumbing store) on the threads of your drain plug...

If you over filled the tranny it will leak out the front bearing retainer.

Muncies are nortorious for leaking out the front of the 1" counter shaft bore. Had luck using a non hardening sealer between the bellhousing and the front of the counter shaft.

Paul, I used a sealer on that 1" counter shaft seal you were referring to. I will start the engine and watch the area for leaks. If I see it leaking from that area, I'm going to seal it externally with JB Weld. I'm not taking that tranny apart because of a small leak.
Does anyone know what keeps transmission oil from exiting the front main shaft. There isn't a main oil seal. There is a large thin flat washer but nothing to keep oil from spilling out if it was tipped on it's end

Not too long ago someone posted a solution to this problem with pics and a tutorial. I cannot find it yet. Many posts come up with "muncie" in a search slowing my hunt.