Flea bay. Not mine, don't know anything about this. Just passing it along. Not a horrible price for NOS. $179 plus 13.95 shipping and any applicable sales tax.
NOS GM 20211820 right T-top roof panel weatherstrip 1984-1988 Regal Cutlass | eBay
The GM part number is 20211820. For Sale : One NOS Genuine GM right passenger side T-top body roof rail weatherstrip seal that should fit the Buick Regal. This attaches to the body and roof opening.
www.ebay.com