It's the "soft touch" coating they use. It's not just an MBZ thing, either - it happens on all cars that used the rubberized coating.

I attempted to clean mine with goo gone, no luck. I eventually use some other product and it wiped off the paint 😔. I now try to ignore it.

I had the same issue. after a lot of research, I used Windex on the soft clean rag. Just be patient and do not rub too hard.

Mine turned out perfect without doing any damage to the button surface

I have the same issue with the buttons on my 2011 R230. I'm going to get them replaced with new since trying to "clean" off the residue just makes it worse. Part of the hazard symbol got messed up with me trying to remove the gunk.

I ended up replacing mine last year for the same reason. I tried cleaning them a several years ago but it came out like crap. Ended up spraying black plastidip over the lock button so you couldn’t notice and forgot about it. Then I made a custom analog clock trim piece last year and my eyes were right on that switch again so I just ordered a new one. So easy and for $75 it made my interior flawless again. Well worth it.

Thank you, KennyK for the tip. I just got an ‘09 SL63 and I was sweating out what to do about those sticky buttons. Windex and a little light rubbing did the truck perfectly! Thanks again.