I had a post about a month and a half ago about a bad hesitation between 500 and 1500 rpm on a 86 420 sel with 180,00 miles. Well here was the problem, after taking it to two different major established auto repair shops in Corpus Christi TX, and more than a week of the car being in their shops, and $1000.00 in parts replacement and trouble shooting, both places were totally stumped!!!!
I got wise and took it to the MERCEDES shop and in less than 5 minutes of listening to the car the mechanic knew exactly what it was,

it was the timing chain, it skipped a tooth on the passenger side overhead cam gear!!!! they had it fixed and on the road in less than a day!!!!

I learned a very valuable lesson, it is, don't be cheap and go for the shops with a lesser hourly rate, YOU pay in the long run!!! in this case more than a thousand dollars than necessary. GO CERTIFIED MERCEDES MECHANICS, HERES TO YA!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!