John,
From this pic, it's not apparent whether that 'shoe' goes inside or outside the hull - but no matter. Pic #2 seems to show the upper stuffing box between the rudder stock and the post.
I suspect that the original sealant got squeezed thin, then the differential thermal expansion (metal vs fiberglass) broke the seal. I suggest you need a real gasket in this location - perhaps neoprene or silicone rubber about 1/16" or 1/8" thick - McMaster should have something suitable. Then when you tighten the bolts, you'll have something to compress. No need to get the fiberglass clean, as the compression will make the seal. Probably don't even need a sealant, but I'd probably use something. Isn't Permatex (the brown stuff) oil compatable?
Best..