You want your tranny to last forever?

Change your transmission fluid (and filter) every 30,000 miles. That is required actually.

I have experienced two problems with my tranny. The seal where the wires go into the transmission leaked. It cost me $1000 because the exhaust has to be removed to access it.

Also the seal on the pan on the bottom leaked. Fortunately, that was very accessible.

Not related, but the valve cover seals are very prone to leaking. Had to replace those.