these are not LED's. these are backlit displays that are
part of the cluster and usually will have some of the pixels or legs of the numbers/letters missing. the "fix" is either sending your unit in for repair or a new cluster. either should be done by an MB specialty shop, as the cluster is easily damaged on removal.
That's a good question and I don't have a good answer. I think it could be expensive if you need electronic parts rather than a wiring or connector problem.
Best thing is ask a MBZ expert, he may have seen it before and have a price or solution for you that doesn't need any expensive electronic parts.
overbis's answer is more informed than mine and I agree that you need to get a Benz expert to handle it.
If you want to find a specialist, here's a directory link for you: