Stripped drain plug in gearbox

[Tomas51]

I've got a 115HP Merc outboard that has a stripped lower drain plug in the gearcase (stripped out by a so-called "expert winterizer"). I'm planning on using a heli-coil repair kit but without breaking off the tang, since I don't want it getting into the gearcase itself. What size is the drain plug (so I can get the right size coil) and has anybody out there ever done this kind of repair? Thanks to all who answer!

[boats.net]

Heli coil doesn't work very well because metal in case is not thick enough to secure it. See if you can find a threaded insert and use epoxy to seal it in case.