I pulled the one fitting on the input side that showed signs of rust and leaking. I suspect I either got a bad fitting or had a really slow leak that allowed rust in over time.
Ended up replacing the one nipple with brass. Mainly because I bought it already and didn’t want to make another trip to HD. I think the worst case is some corrosion between the brass and steel interface point at the tank. I don’t plan to ever remove the brass so will probably be ok … plus I have that anode rod protecting things.
I will flip it over (only a 6 gal) when I get ready to take it offline to drain … that should be good enough hopefully.