if you used ordinary bondo that may have been the problem. i have heard that it "attracts" water. the fiberglass or aluminum bearing bondo will not (supposidly). now you also have to be careful about putting bondo on metal that is not bare. it will, i think, eventually release. anyway hopefully it will last longer than last time. a compromise might be to do the rust binder then sand it so that your filler will bond to the bare metal areas and the pits will be bound with the rust binder. rust is a devil!

tom w

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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.