This firm gray rubber seal is installed in sliding windows on classic Airstream and Argosy motor homes.
It is used only in the cab section of the motorhome. It is installed in the center mullion of the sliding window and acts as a seal where the two pieces of glass slide by each other.
Sold in 3-foot semi-rigid lengths that can be cut to length. Typically one is needed per window.
The center mullion of the window must be removed to insert this seal.