The bolts on the return head rotted and I replaced them with new stainless steel bolts and nuts. (This occured becuase Raypak used the wrong size gasket to seal the header onto the tube bundle).

I still see a small amount of condensation on the tube bundle which leads me to think the bundle itself needs to be replaced. It will cost me $600-$800 to replace this part and I am hesitant to invest so much into this heater. Is it OK to continue to run the heater with this small amount of leaking?