Our M28OI has a 22-gal Monel tank (1978, mfd by Allcraft Mfg of Cambridge, Mass), and while it isn't painted, it has some kind of grey-green stuff all over most of the outer surface. I recently removed the tank to rinse out the sludge that has built up over the years, and not being one to leave well enough alone, I decided to sand and wire-brush the outside of the tank. It would appear the "stuff" on the surface is/was some kind of corrosion, because the surface is etched a bit where the coating was thickest. Seems odd, 'cuz Monel I supposed to be impervious to darned-near EVERYTHING! So, here I am with a nice shiny tank! Do y'all thinks it'd be better to leave the outside bare, or should I paint it? And if I DO paint, what'd be the best primer to use on monel metal? Jim s/v, the Merry Bee