Tell me why we don't use a sealer on transmission pan gasket
 

I noticed that there are a lot of postings about transmission pan gaskets leaking. The problem is that the pan is over torqued, and the pan gets deformed. It is common practice not use a sealant when putting a transmission pan on. This is understandable since it might be hard to the get the gasket maker off the transmission and the pan. However, in the case of a deformed pan, would it not be better to carefully put sealant on the gasket rather than buy a new pan?

Why would it be better?? The last thing you want is chunks of sealer trying to float around thru your tranny. Replace the pan or let it leak.

Transmission pan sealer
 

If your transmission pan is not deformed, then clearly you don't need a sealer. However, if you already have a deformed pan (and it's a slight deformation), I see no way that using a sealer on the pan poses any risk that the sealer will contaminate the transmission, as long as you don't over apply it. I think you are right, the future removal of the pan will be more difficult, and you will have to be careful in removing the gasket residue at that point, so that none of the residue gets into the tranny.