I experienced the same problem a few years ago.
I took the CCU out and resoldered the connections where the pushbuttons connect to the circuit board. It was a cold solder problem, in some of them I could actually see the crack in the solder.
No problems since then.

My 0.02 cents.

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1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
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