Ok, so in the vain of actually answering the OP's question, I dont know that there is anything available. It seems that the best bet is a complete replacement board with multiple LEDs. I have wanted the same thing. The stock lighting on the older Mercedes is weak. (Especially the left rear tail lense....LOL)

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83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.