I've never looked much at the gasket on mine which is probably gone. There's only a very small recess(1/8 or so) cut around the outer frame that I assume some sort of gasket was fit to. Because of other cockpit leaks, I never worried about these drips. The manhole is over the deep bilge behind the engine and transmission so it's not a problem letting gear get soaked in rain.

I use it often, nearly every time we get on the boat. It's an easy visual check for many things related to the engine and steering, stuffing box, exhaust, hoses, seacocks, etc.

Here's one of the same covers in an Alden Caravelle. You can see the screws in the frame -with a flat spot to allow on and off- that tighten the cover into the frame to secure(it can't come loose if tightened).

This boat has been lavishly restored. It has fresh nickel(or something) plating on the old bronze including the pedestal. Curious that they plated the manhole rim and not the cover itself. The covers are built to accept wood decking that is screwed in from underneath through pilot holes. My cover is heavy, about 20 pounds or so. It's a good piece of the old boat, I appreciate it's function.