Improved gasket & fastening the key...
D&C:Removeable cockpit soles to aid engine access used to be more common (e.g. Albin Vega, Hallberg-Rassy 35 and Monsun - and these boats were intended for offshore ocean crossing) and is a great feature. In addition to your gasket probably being past its useful life, you are likely not to have a long-lasting fastener system for holding it down.I don't think I'd like to raise the sole 2" as mentioned in Ed's link tho' the fix described there sounded permanent enough. Consider visiting a local rubber products vendor (e.g. in our area it's the Goodyear Rubber store, which is not a tire shop) and see what kind of HD rubber gasketing they can offer you. After cleaning up the mating surfaces (which may require some minor eposy fairing work on your part), look for a way you can anchor female stainless fasteners either into or underneath the flange in the cockpit sole on to which you place the hatch lid. You may want to visit a fastener specialty house to get the widest selection of products. I don't think the idea of conventionally bolting the hatch to the flange is adviseable, as it will make access to the engine much more difficult and the benefit of this arrangement should be easy engine access.Jack