For some reason I suspect the heater core. I can't find any leaks on the back of the head or block (tough to see, of course) and it's only a small amount..Anyway, I'll get around to checking that. I don't like to use radiator sealants but I have in the past with success. Of course, I also completely blocked the radiator in the hideous old mini-van with one as well! Not a big deal, just one of those annoying things for the "list". F