I’m having a problem with painting a set of exhaust manifolds from a Chevelle 396. I sand blasted both manifolds and painted them with your high temp exhaust paint in the spray can. After a month (car still not started or run) I had some surface rust starting to come through the paint. I took them off the engine again and cleaned them up and sprayed them again with the cast grey exhaust paint. After running the car for 20 minutes and shutting it off, a few days later both exhaust manifolds are covered in surface rust already…..What the heck am I doing wrong?? I used the exhaust manifold paint on other restorations and the paint lasted months before I had to tough them up, but it was from a pint can not the spray paint.