Just did the repair on the odometer this afternoon on my 87 190E 2.6 with 77K on the clock.
As some of the other post, fairly simple job once you get the speedometer out.
The wheel on the far right is slipping, which controls the other wheels. I took the small shaft out with the little white gear on it, carefully sliding in a small drill bit at the same time. Once I had the little shaft out, I made some knurl marks using a pair of vise grips on the area of the far right wheel, then with the aid of a small hammer, tapped (beat :-0) the saft back in.
Got the speed odometer back togeather, and put in the car, and every thing worked great :-). Biggest problem I had was getting my big hands in the dash to unhook & re hook the left AC vent hose going to the left vent.
Other, than that, "fairly" easy DIY job.