On several cars I've owned over the years, I simply used Barr's StopLeak when the heater core began leaking. I followed the directions to a T and it worked fine. At least one or two of them were semi-beaters.
Once when one of them began leaking again a coupla years later (I think it was my semi-beater '84 Ford LTD II), I just disconnected the heater hoses from the core, made a bypass loop, and used the car for several years without a heater. It was only a 4-5 mile trip to work. It was a piece of cake to wear enough of a coat to stay warm for that distance in the morning here in SC.
I opened the vents and cracked the windows if the windshield began to fog up.
When the A/C went out and I got an $800 estimate to fix it, same approach. It was cool enough on summer mornings to make that 4-5 miles and in the afternoons, it was all windows down... no problem. That thing has cloth seats, which helped... it was an ex-sheriff's investigator's car... 5.0 Litre.
That's water from a wash job... not a busted radiator.
