Had the same problem, just did mine a few weeks ago. You need to get the 1.2W bulb(s) at the MB dealership. I say bulb(s) because there are two that provide the backlighting for all three displays. They run a bit over $6 apiece. Each bulb is permanently mounted in a light blue twist-off housing, impossible to find at the auto parts stores.
I bought a set of instrument cluster pullers @ FastLane ($15), and it makes the job of removing the cluster easy. Just be very careful and take your time...I didn't, and one of the tools slipped and caught the plastic cluster lens, cracking a huge piece of it right off! That mistake cost me $327 for a new lens at the dealership!!
You have the electric speedo, so no messy cable to contend with. There are four wiring harness plugs to remove in order to completely take the cluster out of the car (especially if you have to replace a broken lens).
This would be a good time to replace any other bulbs that are suspect as well. I had four that needed replacement...