This seal is used for some vent glass seal and quarter light seal.  If this one is similar to what you require but not exact please see item# S-101 or S-108 Sold Per Foot 1947-1955 RR Silv

Various Coachbuilt bodies where weatherstrip glues into channel on the body (not lid) Furnished Longer for Coachbuilt Models 1946-1955 Some Coachbuilt Models, 1959-1967 Phantom V...

This is a Vent Window Rubber also used on  some rear quarter windows.  Slides into frame. See Part#'s  S-105 & S-108 for other rubber.  1947-1955 RR Silver Wraith, Silver...

Vent Window Rubber also some rear quarter windows.  Slides into frame.See Item# S-105 & S-101 for other rubber. 1947-1955 RR Silver Wraith, Silver Dawn & Bentley Mk-6, R-type Coachbuilt...