Mr. Smith and others,
IF the surface we are looking at in the pic is aluminum (ie: non-ferrous), the problem is specifically from natural electrical action to corrode the material. IF that is the case, the original surface should have been anodized so as to decrease the action but would be better to use a sacrificial anode in the cooling system as well. IF originally anodized, any scratch through the finish accelerates the problem. IF the surface is supposed to be ferrous, it is surprising that it shows no ferrous oxide (rust) residue. So, it appears to be non-ferrous.
Either way, there are no negatives to use a sacrificial anode in the cooling system. Those type anodes are available at any hardware store or at Lowes, Home Depot, etc.
Regards to All that like this kind of stuff,
HB2
Dissident