This is a DIY Video on replacing a Valve Cover Gasket on a Mercedes Benz CLK 430, 2003. This is a pretty easy job, and these gaskets tend to go bad on these cars overtime. 
Make sure that the surface area is clean prior to beginning the job, as any particles that fall into the engine when you remove the valve cover can cause issues.
I usually throw on a little red gasket maker as well with the replacement gasket, just to give it a little extra length of time and so that it seals better.