OP...first, see realoem.com for PNs...very often it'll list dimensions of bolts...not sure of plugs, but I might have an extra lying around I can measure.
Second thing is that you might start by just chasing the threads with proper sized tap. It's not in there very tight and the seal comes from the crush washer, not the threads, so there's a decent chance you'd have plenty of torque to hold it sealed...maybe a dap of rtv to be safe.
Just a little burr could be enough to throw it off and you could easily get lucky...before you go the timesert route.
Also, they do make oversized plugs and you'd be able to just open up the threads a little more and be good. Maybe you need to drill out cleanly first, but I don't think so...not if you're just opening them up a tad bigger. That's sort of a guess...you might have to start basically fresh again with clean hole...but again, you don't need a lot of torque to hold a seal there.