The trans plug will strip if a new crush gasket washer isnt used when its reinstalled, unless it gets very carefully hand torqued. The bolt is softer than the pan, a new bolt should but try ans flush out any shavings that might gave come off or poke a magnet around the hole or something.
well sorry to say but I never seen a washer of any sort on it. For the very little time that I had to move the truck from parking space to work space (50-100yds tops), I used the stripped bolt with a rubber grommet and I pushed the screw in with all i could and turned it about 1-1.5 turns and NO leak what so ever. But I bought a longer bolt with the crush washer from napa