I have a THM350 in my '81. Ever since I've had it, it leaks ATF from the hole in the bottom of the "dust cover" on the bottom of the bellhousing.  A couple of days ater driving it, the puddle is typically about 3 inches around.  Anyone know what the common cause is for this?  Other than the drops on the garage floor, think it's anything I need to worry about?  I am assuming it is a seal on the torque converter or the front of the tranny, either one requiring separating the tranny from the engine, so I figure I will let it go if no worries and the leak doesn't get bigger...

I also plan to install a Transgo or Superior shift kit real soon, if that changes your suggestions on the above.

Thanks!

With the leak you describe, it is the seal at the front pump/torque converter.  The only cure is to pull the trans and replace it.  Be sure to inspect the converter and bushing in the front pump of the trans.  If either is bad, the new seal will leak.

The shift kit may raise line pressure, but will do nothing to cure the leak.  If fact, with higher pressures, it may leak worse.

A leak is a leak is a leak I agree with Ken about it being a front area leak. Could be TC, seal, or the o-ring that goes around the pump. Don't really make much difference; ya still gots to pull it to correct it When it's out, check the surface of the TC hub carefully for any scoring, or a groove. One other suggestion...before you pull the unit out, take the dust cover off, start the car, and look under it at the flywheel, to see if the flywheel is not flopping around. This would make it leak, also, and would require replacing the flywheel. I would go ahead and just completely reseal the thing while it's out. As far as "shift kits" are concerned, I really like the Superior brand. Very adjustable, easy to install, and they do what they say they will.
Don't ignore it.....it ain't gonna fix itself, and you don't need no surprises Adams' Apple38514.8120023148