I had the same problem on our 2006 SL500. Trunk release button too. I ordered replacement switchs online from a MB Dealer (best price found) and installed them myself. It does require removing the inside door panel/card. It's fairly straight forward. There are YouTube videos showing how to do it. There are probably some on here also. The biggest issue I had was getting everything to line up when re-installing the inside panel.

 

I think this is a common problem. Mine broke, too. The switch cover has plastic "ears" that snap onto plastic "tits" on the housing that it pivots on. The plastic ages and breaks. What I did was to drill a tiny hole through the housing and switch and insert a piece of stainless steel wire to make a new pivot axle.

 

In the end I couldn't find anything about replacing the switch cover so bought the switch assembly on eBay and replaced without much issue reading door panel removal walkthroughs. The only catch was it taking a bit to figure out I needed to remove the T20 bolts beneath the pull handle inside the panel.

 

I looked for a replacement switch for about a year before I gave up and just bought the whole switch assembly.

I even tried to re-design the switch in 3D design software and 3D print a new switch, with no success due to the complicated design of the switch attachment.

My indie mechanic said it was really difficult and charged me something like $200 for the job.

Dumb, but now it's fixed, and I'm extra careful with it...

 

Definitely cheaper and easier to replace the whole switch assembly. Find mine on eBay.

 

I had the same problem. As Rudeney said before, the problem is the eyelets the switch button snaps into break.

My solution? 50 cents. I put some VHB double face tape on the back face of the switch button, put it back in place and pressed it backwards to make sure it sticks to the inside wall of the housing. That holds the switch button in place., and because the VHB tape is 1.5mm thick, it has enough flexibility to allow some movement.

To work the switch, you just have to use your thumb to hold down the back of the switch while you gently lift front with your index finger. Pushing down doesn't require you to hold it down, but it's good practice to do that anyway. I had that on my old SL500 for 3 years and it never came off.

FYI, you can buy VHB tape from most hardware stores or Amazon.com