Hello, A couple of questions...

The best thing, if you are planning a full boogie resto (meaning painting inside and out like the factory) then you will want to remove all the old sealer, then work the metal, then spray with an etching primer, then apply the sealer, then paint. The factory applied it before the body was run through the primer dip, and I've found rust in the bare metal underneath. So I always shoot primer first, then seal it.