[grumpyunk]

I tried a helicoil copy that came with drill, tap, inserts, and was not pleased. The metal of the case(SG 250) was so thin it was easy to get the tap cockeyed even after drilling to the next size to clean up the damaged threads.
I ended up taking apart as the 'tang' broke off and fell inside........ it ended up being on the floor of the pan, so it would have been alright.
Doing it again, I would tend towards drilling and tapping to the next size up without using any insert. The insert inside was all wriggly after installation, which may explain the 'lean' of the drain.
I even considered using the rubber plugs that squeeze down to seal.
It was stripped when I bought it, and the PO was insistent upon trying to get it to thread, so stripped out even more...
not fun.
tom