1959 black 270hp (9/2/69) 1981 Beige L81(10/20/80)
I think they are more intended to swell the front and rear seal to stop leaking. I've never had much success with these type of products though. They seem to help some for a limited time. I'd try to snug up the bolts on the leaking gasket without over tightening. Sometimes they are not tight enough or become loose due to gaskets shrinking over time. If it's just the side cover gasket that isn't too terrible to replace without pulling the trans.
Thanks for the replies. I rebuilt transmission 2 years ago and it's weeping at the main gasket on the bottom. I had a so call expert tell me sealant was not needed if metal surfaces were in good condition so I didn't and here I am. It's not that bad of a leak, just a weep but I hate leaks of any kind. I was told if you don't have leaks you don' t have a corvette. I do not buy that. I would never put stop leak in a radiator due to small tubes getting plug, but trans does not have small areas.
Not sure which gasket is the "main gasket" but Muncies have paper or fiber gaskets between every part. The guy who told you to put that trans together with no gaskets or sealers is, indeed, a "so-called expert" rather than someone who actually knows about transmissions.
As others have said, don't use stop leak products in anything you want to keep in good condition. Plus, I've never heard of a stop leak for manual transmissions which use an SAE90 gear lube.
Your best choice is to pull the trans. Tear it down and reassemble using the proper gaskets.
Actually...what you oughta do is go find that freakin' so-called expert and make his sorry ass pull the trans and fix it.otfl