Need your Model M controller.
The controller in M died out. Some keys no longer work 
The M I have is a silver label 1391401 from 1988
Shipping is to Malaysia. Payment with Paypal
Kaiserreich, I think it's a rivet popping problem. When your kb has lost too many rivets, some keys no longer register because they don't hit the membrane. Why don't you open the back and take a look?
I don't have a spare controller for that layout anymore, what a pity. Gave it away. And shipping from me would have cost you only a few bucks, too!