I am working on cleaning up the trunk seal area for my Porsche. I am looking at using Rust Encapsulator to paint the channel for the seal. The channel has some rusty areas (pickled galvanized steel), old paint over the majority and bare galvanized steel in some areas. It is ok to paint the Rust Encapsulator over the old paint or do I need to remove it all. It is all nice and smooth, but rather not sand it down to bare metal.