I'm with Honeyman. Replace the cap with
aluminium. I would use smooth rather than diamond plate, for looks, and for less chafe on your gear. Fill the crack with epoxy putty first, but don't worry about it too much. Just get it sealed up.The cleats and tack fitting have enough bolts to hold the new cap to the boat. You may need longer bolts if the aluminium is thicker than the cap. There should be backing plates under the cleats already. If not, add an aluminium backing plate big enough to take all the cleat and tack fitting bolts. You could add a bow roller while you're at it. Just weld a couple of pieces of 3/8 or 1/2" plate to the top of the cap so they stick out over the bow, drill for a bolt, and use whatever roller you like. I have used (the harder type)rubber trailer rollers on several anchor rollers, and they work fine. You can keep the cost down if you get the aluminium and cut the top piece yourself with a sabre saw, then take it to a welding shop to have the lower lip welded on, and sand it smooth yourself with a grinder. If you can afford it the welding shop can do it all quicker then you can.