Microprocessor buttons on cassette deck fix

Hi,
I have a great Harman Kardon 3 head cassette deck (TD392). Unfortunately, a couple of the microprocessor control buttons have popped off. Today, a 3rd button popped off. The deck is still usable but the rectangle buttons give it the proper cosmetic look. Anyone else have problems with this happening on their HK cassette decks that you know what I'm talking about. What have you used to hold them on?
TIA,
Lou