I put LED's in my 84 & 85 300D. I used cheap Chinese ones from ebay. A few failed, but most are still working after ~3 yrs. A couple things of notes:

Some LED's have contacts which will short out the M-B bulb holder. That will smoke a trace on the cluster's circuit board. Look close and test w/ an ohmmeter to avoid.

Some LED's will not fit, even though sold as the correct bulb#. I recall this was true of some small ones for the push-button switch. They have a square board which doesn't quite fit in the round hole.

For the light tunnels in a W123, use LED's w/ forward shining diodes. Those light the speedometer much better than incandescent bulbs did.

The current draw of the "BATT warning" bulb is used to boot-up the alternator, along w/ 2 other dash bulbs. My LED's don't draw quite enough for that, but once I rev the engine >1200 rpm, the alternator boots-up and the bulbs go out. That is probably due to residual magnetism in the armature. If that bothers you, use an incandescent bulb there.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans