What I am suggesting is that if the tint has covered the area between the combar touchpads and the glass, that maybe the tinting can be trimmed so the combar can make contact directly to the glass as original. I know the metallic tinting can cut down on radio reception per an MB service bulletin, but possibly if I am correct and the tinting is preventing the combar from touching the contact areas on the glass, that trimming the area will at least make the AM reception acceptable.
I feel your anguish. The Buick I bought this year has an rear window antenna also, and the AM reception is pretty lousy. I like listening to talk radio to and from work.