In the process of preparing the body of my car I noticed that most of the cage nuts that are used to bolt the rear fenders on had what appeared to bea thin rubber gasket between the cage nut & the body. Was this to seal from water splashing on them & seeping into the trunk & rear seat areas? Is there a vedder that sells these gaskets or will seam sealer work just as good?

Thank You

Use a sealer but not silicone as it promotes rust.