Trying to change the plugs on my 1999 ml320 and having some difficulty. I'm using a long bar plug spanner but am having to exert quite unusual force to free the plug and I don't want to break something. I wondered if somehow the conventional spanner is jamming. Is there a special plug spanner required or will I just have to force the issue? Any constructive help appreciated . . .

if they are tight just turn them slowly they will free up, use a short as extension as you can get in there as close as possible.
here is a link to the tool for the boots. it is actually a bent 17mm wrench. if you order the tool from mercedes they will send you a valve adjusting wrench from the old m110 motors which is mercedes part number 110-589-01-01-00. i have it and use it everytime i do the plugs on a 112 engine works great. the tool for the plugs is 112-589-01-09-00 it looks like a conventional wobble socket plug. what plugs are you using? if you have mor questions or need more info email me. i also have the service sheet for the ML's i can send it too you, too bid to post here
Ray
mercedessd@cox.net

plug boot tool

If your plugs are original then they will be difficult to get out. The plugs are good for 4 years or 100,000 miles (which ever comes first).

Like Carson356 suggested, use a short extension and turn them slowly (ease them out). Take your time doing this or you may end up with broken plugs - also make sure the engine is at room temperature (not warm or hot).

I prefer to use dielectric grease inside the boots and high temp anti-seize compound on the threads - it makes removing the plugs easier the next time they need to be changed.

__________________
Ray
1998 Mercedes E320, 200K Miles
2001 Acura 3.2TL, 178K Miles
1992 Chevy Astro, 205K Miles

Thanks for taking the time and trouble to post your helpful advise. Other chores have kept me from tackling the job but I'll get round to it in due course.