Vintage Synth Repair

Hello,
I have a Fender Chroma Polaris synth that has nine buttons that do not
work.  One of these is the "lower function" buttonn which is particularly
important.  These buttons are the membrane type with a flat pannel, and
buttons that don't move when you press them.  does anyone have any advice
on what the best way to fix these is?

I am also having MIDI problema with this synth.   MIDI note off messages
are percieved by the synth as being note on messages which subsequently
sustain indefinitely, not acceptable.  Any suggestions?

Thank you all,

Kalani Dix