Changed the transmission fluid, filter, and pan gasket in my 85 300TD on Sat. I bought cheap Dexron III at Wal-Mart (Super Tech). Following the DIY's on this site, I drained the torque convertor fairly easy and I also drained and removed the pan without much hassle. I did not torque the drain pain, but I tightened the bolts in a criss-cross pattern, and after filling with the appropriate amount of fluid (once again following the DIY's on this site), I checked and found no leaks the day after.

Fast forward to Monday night. I had a change of heart on the Wal-Mart fluid so I went out and purchased Mobil 1 synthetic ATF. Drained the torque convertor and pan again, but I did not remove the pan or change the filter. I measured exactly 5.2 quarts of drained ATF fluid. As I was pouring fresh quart number 4 into the transmission dipstick tube, I heard ATF fluid gushing out of what seemed to be the top of the transmission pan. Yes, I did replace and tighten the drain plugs on the pan and torque convertor. The leak seemed to be coming from the gasket, but I couldn't pinpoint it as there was fluid all over.

Did Mobil 1 ATF cause this leak or is my stupidity to blame here? Why didn't the gasket leak when I first changed the fluid? Was it wrong not to change the filter?

Frustrated and ready to give up on the home mechanic impersonation.