Are you talking about the quarter window or the main window ? The one on main window inside the door from memory, (Mainly stops it rattling and helps push glass against outer seal, to seal) is felt not rubber but may be reproduced in rubber now. Anyway pretty sure that is the bailey channel rubber, there inner and outer. Or the other is quarter vent seal. Bailey channel kits and quarter vent kits are on ebay but i have no experience with there quality. Otherwise try peter jacksons, old auto rubber.