My neighbor has one, going on 17 years with stainless and regular steel, I've had a none stainless and my current one is a stainless 450 (10-12 yrs old ). They all seem to suffer from cracks where the bottom tubes are welded to the wall ,at both ends. I have patched mine from the inside, but would have to cut out the outer tank wall ,to get at the old welds to fix the problem. I like these 450's ,they do the job .
J 5