Sea Ray

I own a 2009 310 Sundancer with 300 hp Mercruiser Axium engines. Recently I lost an engine returning to my slip after a long trip. I had my marine services company look at the engine and they discovered that salt water had entered one bank of the engine and caused the engine to seize. According  to them, the engine needs replacing as it is almost impossible  to remove all the salt. After draining the engine and cranking the starter, salt water continues to enter the cylinder. Risers and manifolds were removed for inspection and were found to be almost new. Anyone else have a similar problem? The engines have less than 500 hours on them but have always run in salt water.