Plastic bolt/screw? Why would you not just use a new proper skeg screw? Again, my concern is whether or not the mating surfaces are flat. The other concern is the new screw’s ability to seal against the mating surface on the skeg. Those screws are behind the spaghetti seal, so there will be an internal water leak if the screw is unable to seal against the skeg mating surface.
I agree with LG, these clam shell gearcases are very difficult to seal up properly. This gearcase has some roller bearings, so it is even less tolerant to water than the smaller gearcases with bronze bushings.
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