I have used the silver stuff that comes in the cylinder many times as a temporary solution. I have not had any negative effects from it that I know of. The main cause of the leak is bound to get worse eventually and require repair though in my experience. I have also used it when I cannot find the source of the leak.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.