Originally Posted by Kieran1

I was thinking something like that, but could not understand why the CE would be the only W124 with it...?
Odd.

Someone else told me it was for spare light bulbs; I don't agree with that guess but he does work at an MBZ dealership...

Originally Posted by RBYCC

The maintenance booklet slides into the slot.
The window matches up with the next service interval page.

How do I know...bought my 300CE new in May of 1988 and that's what is still in my windowed slot !