The buttons are stuck in dry lubricants.
Pull the knobs off, clean both sides of the metal blade for each knob and the respective
mating slot in the knobs plastic backside.
Contact cleaner can often help dissolve and shift the dried stuff.
Sometimes IPA is better. Try and see.
Pipe cleaners are good for cleaning both parts as they can be shaped to suit and will fit nicely in the slot.
When clean add a little silicone grease (of the non-hardening type) to the slot in the
plastic backsides and push back the knobs.
All this can be done from the front.
If a knob is really stubborn, you can lever it off careful using a flat-bladed screwdriver
from below into the knobs recess and against the front frame with pieces of thin cardboard between to avoid scratching.
Martin
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