i bought the chevette heater core for my radiator and when "sweating" in the fittings a bead of soldier went in the radiator and i can hear it rattling around and i cant get it out. am i screwed ? will this cause corrosion ? im going to try flushing it with water to get it out tommorow. any knowledge on dissimilar metal corrision or otherwise would be appreciated. also i used 3/8 fittings instead of 1/2" cause i had some, are these to small?