I have yet another thing to fix in the white car. The heater core is leaking, and it seems to be getting worse. There is a coolant smell in the air when I run the AC or just blow air, and it's getting stronger. I found some info on Youtube, and the job doesn't look too hard. I'll update this thread when it's done. I just happened to have a spare heater core that I bought years ago. I'll leak test it this way: I'll fill the kitchen sink with water, submerge the heater core, stop one tube, and blow in the other. Hopefully, I won't see bubbles.
Edit: The replacement heater core checks out -- no bubbles. It's a used one I bought off Ebay, so I had to check it.