Officially Official: 2012 Third Generation R172 Mercedes-Benz SLKThe new SLK is officially on sale. Mercedes is taking order this month for the hot new roadster. The SLK will be offered with a direct injection version of the 3.5 liter V6 putting out 306 horsepower. This SLK350 will be the range topping version until the AMG version hits sometimes later. SLK200 and SLK250 versions will fill out the rest of the range.