I have heard from a friend, that he sprayed some brake cleaning fluid down the cable from the top end( after removing the end that goes into the meter) This will loosen the gunk and then spraying some graphite lock spray of silicone oil in there.
He fixed it this way and it worked for him 2 years until he junked the car.

Just give it a shot.

MVK

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One penny saved is three penny earned.

1985 300D Turbo 179,000miles