Is this the coupe version or the four door? My parents had a matching pair of the coupe, one 6spd and one auto. They both had their fair share of problems (luckily covered under warranty) but never broke down on them. I got to drive them fairly often, almost daily. I wouldn't consider them Mercedes quality as the entire car just didn't feel quality, from interior to exterior.
While they were at Mercedes getting fixed, I got a chance to drive the four door rentals which proved to be an even worse experience. Pretty boring, underpowered vehicles I'd say.