I had this problem, poor reception on both AM/FM Stations. I thought it was a antenna problem and checked all the leads, still
poor reception. Just before pulling the radio I thought I would check the antenna on the fender. Short story, removed the corrosion from the threads and corrected the reception Problem.

 

I was just going to suggest that you try cleaning up the antenna itself, but... Grounding is really important for good reception. I have actually seen old antenna wires that were scraped through to the conductor cause reception problems too, just for future reference.