This past spring the heater core in my 77 was leaking, so I bought a NOS aftermarket heater core off ebay as a replacement. I pressure tested it on the bench before installation and everything looked fine, so I put it in. Unfortunately, joy was short lived and by the end of the summer, the new one that I just put in was leaking. Again. Direct drop in cores are getting hard to find, and are expensive, so I started messing around with alternatives. I've been reluctant to mention it because th