I'm afraid your switches are dead.
Since they're not on the same column/row of a mux and have the same age as mine ( DX and OBXa ), I suppose your only chance is to take the circuit off the panel, gently remove the switch cap with 2 screwdrivers, one left and one right and then lifting it, sand the silverplated ( sigh!! ) contacts with 800 sandpaper and put the caps on again.
Now you should be ok.
Just test them before : a multimeter with a beeper connected to the 2 pins of the switch should sound if the contacts
are ok. Try it 2 or more times.
If it beeps than it's ok and you have to search elsewhere.
If they do not beep, prepare to remove the knobs, the nuts and then unassemble the switches as described before.
I just desoldered ALL off my 2 oberheim DX switches, removed the caps and cleaned with soap and water, sanded all the contacts, changed some burnt out leds.........and theyr resistors!!!!!!!( they were too bright! ), reassembled and resoldered : long job but now both work like new.
Enjoy and Good luck