starter failure honda 130

My starter failed on a my Honda 130, which I then replaced. now after one month this starter seems to have failed. BUT, with a light tap on the starter it will engage when the key is turned to start, but then the starter may not disengage with the gear until a few seconds after the engine starts. When I replaced the starter I noticed a fair amount of marine buildup (not corrosion) on the large gear that the starter engages. This gear is below the power head ad I believe saltwater can get in. I this normal? I keep the boat in saltwater but flush with fresh water after use.... thanks for any help