Since last year, I have lost almost 3/4 a knot of motoring speed. Engine (21hp Universal diesel, 1983) runs great and holds RPM. Everything else seems the same. My only change was applying Micron CSC bottom paint over the winter instead of the traditional copper based paint. I noticed the slower speed as soon as we went in this spring. Could it be a slipping clutch? Could the paint be slowing me? I checked speed with a GPS and know it's correct. Thanks, --Mark