Darn, Richard we really thought you had a valuable pre-production car there. And yes the first MB diesel would have been about 1936, but the info I have seen indicates that the model number was 260-D.

On the earlier cars, 123's, there is a central bulb mounted down in the console which has fiber optic lines to a lot of the various switches above the ACC area, but the ACC unit itself has four actual bulbs mounted on the back side.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150