LED bulb may work by reversing. They have + and - contacts. There was a ebay seller making custom (plasma?) lighted dials.
The LED bulbs help a little.

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Present
1987 300SDL
1991 300SL
1990 560SEL
2001 ML320

Past
1969 200D 1979-82
1983 300SD 1984-85
1972 250C 1982-02
1995 S350 2011
1997 S320 2012