I'm thinking of trying something different for the two sides that have some soft spots were the chain plates and all were not cared for right byt the privous owner. Instead of just cutting off the top lever and lifting it and replacing with marine plywood and epoxy here is my idea.
They make a new shredded rubber mulch (from old tires is my guess). I have mixed up a sample batch of it with epoxy into a sludge paste Sort of like OSB board ( shredded chips and glue) I made a test square of 1' by 1' and 3/8" thick. It weighs about the same as the marine ply embedded with epoxy top and bottom.
My thoughts are straight epoxy is heavier, cost more, and nothing to stop a crack from running. With the shredded rubber in the mix it should stop runs like osb board or when they place fiber in concrete. Drilling holes would not expose any wood. If water got into it, it is epoxy and rubber so water would not cause issue. Also the paste would flow easier into the cavity and make a more complete surface and then replace the top layer on it.
Am I missing something in this idea? I'd appreciate comments. I know it is different but can't see a downside. Cost is not much more then plywood and epoxy on top and bottom.