mzsmbs: You should ONLY fill the rad to the top of the indentation (facing the engine). You can see it inside, if you can't, it's probably too full.

Peter: It's a bad solder along the top. The rad was a replacement a few years back and I believe that they resoldered it, possibly recored it, and it was a bad soldering job along the top. I went all along the front the second time, redoing the entire joint, and it's fine now; but the edges are the problem points now - they didn't leak and I didn't feel like unsoldering the support brackets to repait them, but I suppose when I fixed the main leaking source, the pressure caused another area to go.

This time, when I take it off, the entire seam is being resoldered. It's a PITA, yes, but it's better than adding coolant often.