Some buttons on my Phillips 'BMW Business' radio/cassette don't work?

Some buttons on my Phillips 'BMW Business' radio/cassette don't work or only work intermittently. I have tried cleaning the contacts using 'contact cleaner' and methylated spirits, but without disassembly as I couldn't figure out how the radio is supposed to be opened up. This didn't work. Any ideas? Thanks, Patsy.

Patsy
April 2009