Re: garboard drain ??
Is it a garboard drain or a transom drain? Garboard drains typically stay wet longer. Did it get the chance to freeze while wet? If the wood or fiberglass is dry, then epoxy the screw holes to tighten them, watch, keep dry and motor on. If it is an aluminum hull then there are some issues that must be addressed.
If you have a heavy hand then you need to learn to tighten just enough to stop the leaks. If you need some pipe dope (the type out of a can, not Teflon tape) to help you it is cheap insurance. I had an employee that I had to restrict to a torque wrench because he snapped so many bolts, three quarter inchers mind you! Those small screws were meant to hold the fitting in place, not to hang your weight off of.
If all else fails, then use a Dremmel tool and grind out the threads of the plug fitting and use a snap over drain plug. That will eliminate all of the overtorquing.
Good luck!
