Send me the pump or scrape off the deposits and I'll tell you its chemical composition. I have XRD, FTIR, FT Raman, XRF, and bulk chemical analysis techniques (AA, ICP) in my lab and readily available for interesting questions such as this
. There's no need to make any allegations until we see what's what. FWIW aluminum oxide deposits wouldn't be orange, and I don't know why there would be enough iron in the loop to make ferric hydroxides (which are orange/brown). If it is a rust then where'd it come from? The magnets I guess?