The '46-'57 Buick Parts Catalogue shows two thicknesses of glass channel filler were used on all models of these years.
Part no 603954 (later 370389) was 1/32" thick x 1-1/2" wide.
Part no 603955 (later 370390) was 3/64" x 1-1/2".
Was not able to find out which applications used which thickness. Looked in Chevy parts books and found the same two items. Offerings on the web look to be a black rubber material.
Maybe this will will narrow the search down some.
What has been, can be again. (Bob Wills, 1942)