I just completed this job in July. It was very easy to do. You must use the proper sealant (loctite 5900?) from the MB dealer or Fastlane. Make sure you put enough in the corners between # 143 and the head. Replace #142 while you are at it. I also replaced the vave cover gasket for good measure. The most expensive part is the sealant
My car is now bone dry for the first time in years.