The steering wheel buttons on Mercedes become sticky as the car ages. This is due to the top protective coat dissolving and degrading over time. As the car ages, the volume up/down and COMAND buttons will look ugly and dirty. One solution would be to replace them, but before you spend money on replacing the buttons, try cleaning them.
To clean the buttons use a cleaner that can remove the glue. You need to be careful because if you use a solution that is too aggressive it may remove the paint from the steering wheel buttons.
Do not use acetone or any solvent that contains isopropyl alcohol because such solvents will dissolve the plastic and the paint as well.
At first we applied some Goof Off Heavy Duty cleaner and let it sit on the buttons for several minutes. Then we used a sponge to wiper off the dirt and sticky material off the steering wheel buttons.
In the end, the buttons looked much better and cleaner. The Goof Off didn't damage the paint in our case.
Another method to clean Mercedes steering wheel buttons would be to use an object to scrub off the tape. This takes longer and you risk making scratches on the buttons. We have seen Mercedes owners even use erases to remove the sticky material.
The last method would be to resotre the buttons by removing them. Cleaning them and repainting the buttons. You will need to cover the symbols with tape so that they don't get damaged.