Per nestork:
Your best bet would be to get a set of dental picks so that you can take
the old O-ring out, and then just put a new O-ring, or one size larger
O-ring in for a better seal.

In the interest of brevity, I lied a little about the o-ring. It's a
custom shape to accommodate a few screw holes.

I think I'm going to go the silicone grease route. If that fails, I'll
just remove the o-ring, set the joint in marine silicone sealer, and
hope I don't need to disassemble it too often.
--
Pete Cresswell