I replaced an evaporator on a G600 Manitowoc some years back for a customer who had a particularly bad mineral scale problem. A few months later he called saying he had just cleaned it but the machine wasn't harvesting right.
I got there and saw the evaporator was all blackened with bits of green. He has used CLR and now that new evap was toast.
About 5 years ago, another customer ruined a Q420 doing the same thing.