I installed one on a '65 Plymouth and never had a problem. Also have one installed on my '84 Suburban w/700R4 transmission, no leaks. On my Dodge CTD I installed a B&M that I purchased thru AutoZone. The new Teflon seals they give you never do "tighten" up like the old seals did, but no leaks. The drain plug will turn if you don't use a back up wrench when removing the plug. The instructions make that real clear.
Do it, I drain the transmission pan w/every oil change and refill with about 6-6. 5 quarts of fluid.