Originally Posted by gtflash
I'm happy to replace with stainless again although I'm surprised by the corrosion.
You were very very naughty to fill that tank with water!
I'm not a metallurgist, but stainless steel requires oxygen to maintain a rust free barrier on it's surface. If the oxygen in that water became depleted it may have effectively created an environment that allowed crevice corrosion to occur. Poly will have a learned opinion on this theory
Personally, if the actual corrosion was superficial, I'd clean it up and polish it and refit the lot with decent sealant. There was a thread a couple of years back when Osprey fuel hatches were failing - a product was recommended? With FUEL in the FUEL tank, a repeat is unlikely