Volkswagen: 1980 VW Radio, fm signals, fm cassette

Question
I have a 1980 Scirocco with a Blaupunkt Richmond AM/FM Cassette.  The AM works fine, the FM only works sporadically.  It won't work for several days (the AM is still working), then sometimes when I turn it on it works fine.  Any suggestions?

Answer
check the ground on the radio and try a new antenna... as long as the antenna you have is not amplified...(which it wasn't from the factory).... I would try a new antenna first.
you can do a search online about fm signals for a better understanding than i can try to explain.
Sorry for the delay,
shad