Well to close out this thread, I expoxied the rreal seal retainer to the roof using jb weld, and it is firmly afixed and ready for a new seal installation. Apparently onlt 3 smal spot welds were used by MB to affix this retainer originally, and given tine and stress those will likely fail. By using epoxy to reattach, it does not interfere with the side rails, meaning those are freely removable independent of the rear rail.

Thanks to all, hopefully this willbhelp someone in the future

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Stable Mates:
1987 300TD 310K mi (Hans)
2008 Jeep Grand Cherokee OM642 165k mi (Benzrokee)