There has been leaking fluid coming out of the tail extension of my trasns so I took it apart to see what it was? I still have no idea what that hole is or what it does? What is it for and why is it leaking? Also can I just plug this hole up?

 

That is the drain back hole for fluid that is in the extension housing. The fluid is coming from the extension housing to case o-ring, extension housing seal or the back of trans or extension housing is cracked.

 

ah no its a 4x4 transmission, the leak was because I thought the tcase adapter (extension) was a dry cavity like it is on the new GM 1500 and 2500 trucks. my ignorance ceases to amaze me.