I used the Calyx Exhaust Manifold dressing found in Ecklers and elsewhere. I applied it last winter, and I have been very pleased with its performance on my manifolds. It looks pretty good overall and a lot better than before I applied it. One tip I have for the Calyx, is that I added a little water once it started to dry out in the container. This made is more pliable and easier to apply. The Calyx is specifically for manifolds according to the ad in Ecklers. I agree with CQRT, I would remove headers and spray them, but for manifolds, I think Calyx is a good product. It is possible that you may have to reapply, however, it is an easy process and not very expensive.