Bought this '68 Riv with the coolant/heater hoses disconnected from the heater core and plugged. PO said the A/C works, but won't for now because "...something, something, heater core bad, something else..." He had no idea what the problem was. It's pretty likely that the heater core is a leaker (no idea if it's original or not), but before I go to the trouble of replacing it I'd like to get some tips on making sure the core itself is the problem. So far, I've run water into the top pipe (thereby back-flushing it) and water came out the bottom pipe - so it's not clogged. But neither did it leak inside under the dash. I have to figure that it still might leak under hot coolant pressure, but I'm not an expert on heater cores. So, before I re-connect the coolant hoses and put manifold vacuum to the heater valve in the intake to open it, is there some last-resort test I can perform to know whether or not the core is bad? I would really rather not have hot coolant leaking onto the new(er) carpet underneath the dash. Does "not leaking" under ambient pressure (the test I already did) mean nothing at all? What are the odds in this case? As always, thanks so much for any insight you guys can share.