2006 SLK280 starter problem
 

I have a 2006 SKL280 that has intermitent problems starting. At times when I turn the key to start nothing happens, just a single click, but does not start. The car will usually start on the second or third try, but has sometimes taken as much as 10 tries before it will start. There are no system errors, lights and dash panel come on normally. I have taken my car in to the shop three times to figure this out and they can never replicate the problem.

Looking for some suggestions before I'm stranded. :(