Is it on your 300 SD? The buttons on my 81 SD were worn and looked pretty crumby. I had some extras, one set from a 83 300 D, and one set from another SD. I tried installing one of the better looking sets, and the left rear window wouldn't work, I didn't want to put the bad looking ones back in and figured that the nonworking one wasn't any good any way, so I tore into it. They are very simple, easy to open up, easy to clean the nonworking points and easy to reassemble. I didn't do anything with the LED's but did notice them. Probably could replace them, do you have access to a Pull-it Yourself type wrecking yard?
If you can't find one, e-mail me and I'll send you one as a Christmas present.