if i were in your place i would try to remove the patch and fix it wo removing the engine. the various epoxies and such are excellent and it it doesnt work you are no worse off than you are now. the key is getting it very clean.

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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.