I have seen so many leaking transmission pan gaskets due to abusive installation - I just have to say something. I saw it again today in my shop - so my rant seems even more appropriate. Take a close look at this picture. Can you see what is wrong with the gasket? That is right, there is a portion of the gasket near the center bolt hole that is split in the middle. The reason for the split is not old age - but rather due to over-tightening the bolts. In this case the bolt was tightened so much that it bent the stop tab over to the side!
Problem & Solution
Common among these chassis:
I had to use pliers to straighten the tabs after cleaning the pan. The tabs should sit approximately 1/8 inch above the lip of the pan. The purpose of these tabs is to prevent over-compressing the rubber gasket. I have seen some pans so badly deformed that they could not be straightened! Sometimes buying a new pan is the only way to solve a persistent leak problem.
When installing the pan with a new gasket, progressively and CAREFULLY tighten all the bolts until the taps just come in contact with the transmission housing (see image below). I like to tighten the bolts until the stop tabs get close - then wait 10 minutes for the rubber to compress - then I go back and complete the tightening sequence. You have to "feel" the tabs make contact. At that point STOP. This is one case where just "a little extra for good measure" is not needed or wanted!!!