I have no idea if it's causing the problem or not, but one thing you can try is the rear window defroster repair kits. I believe they come with some kind of pen with conductive "ink" that might be enough. Unforunatly I'm not to sure how you'd undo something like that if it proved to not be the problem or caused more problems. Perhaps try bridging the gap with tinfoil or something else conductive and see if your reception improves?

Matthew