npeters, I haven't fixed a tranny housing with JB Weld, but I did take care of a smashed 2002 EX oil pan with JB Weld.
I had our new Ody up on a jack for its first oil change, and that el-cheapo 2-ton jack twisted, broke, and impaled the oil pan. Luckily, it didn't break the oil pump pickup. The broken metal was in the shape of a letter "T" (where the aluminum was fractured). I managed to pull the pieces together without breaking them completely off, cleaned it completely with brake cleaner, rough sanded it for adhesion, cleaned it again...and on went the JB Weld.
I had no worries about draining any oil prior to the repair...I'd drained it all out first by pulling the plug, and when it fell off the jack, the rest drained out the hole I broke into the cast pan.:stupid:
It held for a week with no weeping until I got the new oil pan installed. I probably could have gone thousands of miles with that repair, but it really was a big compound fracture in the cast aluminum...a hairline crack it was not. This was the first time I'd used JB Weld for this sort of thing, and I was really impressed by the way it handle the heat cycles from cold to hot to cold every time we drove it.
The key here will be to drain that tranny completely, then prep and clean the repair area as much as possible before applying this stuff. When it comes to surface application of epoxies, cleanliness and a properly roughed-up surface and following the directions on the JB Weld package are your priorities.
OF