You might try Gluvit or there is another product call "something" Creeping Crack Cure". both available at "Boaters World". These are thin resins that supposedly will seep into a crack or void and then harden - thus sealing the leak.
probably worth a try.
I replaced my teak toerails with IPE - a very dense and durable wood - actually used for the wood on the Atlantic City boardwalk - suposed to last 20 years or so untreated.
