Vintage Synth Repair

After recapping of four electrolytic capacitors in power supply and  
cleaning this machine I have following problem on X911:

- after switching the instrument on the Led [D35] on button  
"Distortion Guitar" [SW10] is permanently on and it's not possible to  
switch it off usual way by pressing this switch (as with all the other  
buttons). Led goes out after pressing the "Cancel" button, and after  
this it's not possible to switch on "Distortion Guitar" button and lit  
its LED. After switch off and on the instrument this scenario repeats.

Am I right supposing that there's problem with IC11 - CMOS 4069? It's  
just strange that three gates in this IC work well, and three  
connected to "Distortion Guitar" button not (or at least one of them).  
Is such kind of partial damage possible with this IC? And could I  
destroy this CMOS IC just by opening the machine, disconnecting all  
internal connectors and doing dust cleaning? All the other CMOS seems  
to be OK...

IC is NEC D4069C, after short research I've found probably this old  
chip is out of production. What would be modern equivalent? CD4069 or  
other?

Or should I check different components which could be damaged?

Thanks for any advice. If you need service manual with schematics, I  
can send it.

Daniel Forro