To my knowledge there is a rustproofing material applied, similar to 5200. It sets up to a semi hard consistency. It's a urethane rubber that requires mixing in a catalyst. After it sets, black paint is sprayed over it. You can remove the layer of paint with acetone and probe the sealer with your fingernail. There should be very good adhesion of the rustproofing. If there isn't, the metal has rusted. Repair is to sandblast to a white finish, apply phosphate based metal prep (phoshoric acid), dry well and then apply the 5200.
