Thanks for the perfect instructions!

I was able to fix “random mode switching” glitch.

Went up to step 16 (skipping steps 12 and 14). Then removed the top panel.

Extracted the scheme and put it into a cup filled with 91% alcohol for 10 minutes. Meantime opened up the plastic part of the mode switcher and applied 2 drops of universal oil. Then took the scheme out of the cup and carefully cleaned it with cotton swabs and alcohol. Sprayed it with cleaning duster. Assembled everything back and so far the glitch is fixed.