Re: 125 force lower unit drain plug
No damage unless you go very far in and touch the shift yoke or shaft. Even then, almost everything in there is hardened; the main thing you need to worry about is getting metal chips inside the lower unit.
Heli-coils are nice and handy, but in this application, I think they would leak water into the lower unit. Better to drill out the screw and re-tap the hole for either a larger screw or a pipe thread plug -- 1/8 inch NPT if it will fit, or if the hole is too large, 1/4 NPT. Just don't tap too deep-- NPT are tapered and if you tap too deep, the plug will go too far in and not seal. Better to tap not deep enough and take the plug out, then tap a little deeper until the plug is just above the gearcase surface when fully tight.
