Vintage Synth Repair

Hallo,
       I've owned a Multimoog from new, it still works but...
I've stopped using it because the key contacts are a nightmare. When I 
switch on about half the keys work. 

I wipe the contact bar with a dry cloth, wipe each individual contact 
wire and maybe after a couple of hours I can get all the keys to work. 
Next day I'm almost back to square one.

It's the only keyboard I've got with this kind of problem.

Either the contacts or the bar must be oxidising.  

Has anyone else experienced this and has anyone any remedies that don't 
involve opening the case up or soldering?

Thanks