no..not yet. I would wager it is the o-ring on the rear servo pin leaking MAKING you think pan gasket.

brake clean and baby powder will tell the tale.

I have brake cleaned it well and rtv the end of the shaft up and let cure. 50/50 chance it seals.

might as well run a wrench on all of the tail housing adaptor to trans housing bolts & adaptor to xfer bolts.

the 727 tailhousing adaptor has a paper gasket but I have found the o-ring on the servo pin to be the most common leak as it is always over looked on a rebuild.

check the NSS plug, the coating on the washer will wear and leak on top of the pan rail also.

have you ruled out the gear selector shaft and PTK shaft seal? again brake clean and baby powder there area this leak shows up sitting over night as well as when driving. so run to temp/clean/let sit over night.

LARRY PM me you # and I will text you a couple pics pointing out the spots I refer to. (pivot pin) then you can pin point them under your truck.