very common. I have brought many cars that have driven into shed and, whattya know, years later "Auto stuffed", selling cheap needs new auto.. all they needed was 3 litres of trans fluid and let it idle for 10 min. trimatics seem worse than T400

the pan seal can be tricky, I use proper trans sealer, I have found the others to leak. always go for a neoprene seal, and do the bolts for the pan up in a sequence to make it evenly tight. do them all up finger tight and allow 24 hours for the sealant to cure, then re tighten 1/4 turn..

overtightening on an old cork gasket will cause a leak for sure