I’m not jedindl but will offer to answer the question. The rack I pulled from a 65 wagon had these threaded inserts (very similar to nutserts) in the roof for the four corners (2 per corner) and one each side for the crossbars. I didn’t notice any sealer in or around the inserts. Maybe they were sealed with the rubber seals (which were totally dried up on the wagon from which I pulled the rack. FWIW those seals are available as a repro).
