i have a misfire on my mecedes and have to change one of the coil packs but they seem impossible to get to.

Try this site-
http://www.aclassinfo.co.uk/mypage.1.htm

They are individual coils that have the plug cap fastened to them .Remove the plastic strip on top of the engine and undo the securing screws and earth braids and just pull them off.

Mercedes are built like that. You have to go to the German mechanics. They did this on purpose. Look in Chiltons if you really want to know. Maybe you can do the job, but afterwards you'll wish you took it to Dieter and Fritz instead.