I had a total of 55 years in the body business, and the only solder I used was Hewett 70/30, which is 70% lead, 30% tin, as squeeze has pointed out...The lead that plumbers use will not stick to metal because of not containing tin, but is great for making fishing sinkers...I still have some body solder, but if I were to need some today it would be a chore to find it, if at all. Solder will not stick either, unless the metal is bared of any paint, then tinned using a tinning paste...Body solder was getting very cost prohibitive, the last time I purchased it was almost $5.00 a stick and that was over 15 years ago...As to what the factories now use on roof to quarter panel joints, they use an extreme high temperature formulated type of plastic that will withstand 400 degree's or more that the body sealers, and sound deadening need to cure before priming...
While working for GM, We had 150 full size Cadillac's shipped in bare metal for Us to bonderize, seal, and bake, then to prime and paint body in white. The roof joints were all done in lead, and after baking for 30 minutes at 400 degree's, the lead all melted and run down the sides of the quarter panels, and that's when they developed the high temperature plastic, which appeared had a lot of brass particles in the ingredients. Sorry for the long winded post, but the only time I found it necessary to use lead was when it couldn't be metal-finished...
