That is a common problem on early W140 chassis with "analog" gauges. The problem is in the MOTHER board that the gauges plug into. AT dealer only option is for complete inst cluster replacement. However there are VDO repair shops that can repair the board for $300-$500.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator