Mercedes Benz repair: 89 Mercedes benz 300E faulty valve, mercedes benz 300e, faulty valve

Question
My mercedes runs, but the 6th spark plug in the engine is covered in burnt oil depsits.  I change the spark plug and in a week, it is just the same.  I took it to a MB repair shop and they told me that the valve guides were bad and they needed to be replaced.  Can you tell me how this is done?  

Answer
This is not a DIY job, the procedure requires special skill/knowledge + special tools.
If the guides are worn out the odds = 98% that the seats/valves are not seating correctly.

I suggest removing the head, and have it serviced correctly at a machine shop.