I've got my 1992 Apha 1 out drive off (first time since I bought her last summer)and am replacing the impeller. There are what seem to be mineral deposits on the inside of the exhaust passages. Is this normal for a system this old? If its in the outdrive I assume it must be in the rest of the system (manifolds etc). She ran fine last year with no overheating issues. Is there anything I could (or should) do to scrape off what I can? I recall reading some post from guys saying that they have run something through the system to help reduce whats there and prolong the life of the risers and manifolds a bit. I'm already into too much money this spring so I'll like to avoid anymore (at least for now). Any advice on what and how is appreciated.