oooooooooookay. do you recommend the dealer or any competant shop?

Who knows today???

I would expect a Dealer to be well aware of problems like that, but some just deny or say they never had any problems ...Don't know why, but they do.

There was actually a classs action suit on those b/c so many needed rings, but the outcome was the owners were not using Factory rec. oil..
That was the first thing I noticed on you post, so you seem to have taken proper and correct care...
Your preference should be with someone who knows Benz,,, as far as a leak-down test , any decent mechanic knows how to do that....
Again , that is the FIRST test I would want to see before making any diagnosis...
Even if you just go to a mechanic for the test alone and the results...that will get you on your way...I would not be as foolish as to make a low compression diagnosis w/o more info than a PSI reading and a guess.

Do a search on this Forum and you will see all the related threads on that engine with your exact condition. And then when you talk to a guy about checking it, you will know if he is not aware or hip, and can then decide if you want to use him.
Just ask if they can do a leak down test...if the guys says "A What? "... turn and run... Any good guy is simply going to say "Sure." .Then you explain your condition and the cylinder you seem to be having a problem with low compression and oil evidence... and that is all he will need to give you a diagnosis that we can not.

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A Dalton

ooookay. Do you recommend the dealer or any competant shop?

Sorry wrong response. But Thanks soooooooo much! I will have it done within next couple of days..

You want someone you can trust - I think most people here don't recommend the dealer only because of the cost. See http://www.peachparts.com/shopforum/good-mb-shops/
for some recommended places.
As to the ring issue on M112/M113, I think that was on earlier 210's because of confusion on the oil-change intervals: people (incl MB Dealers) let non-synthetic oil go too far (like > 7500 miles) between oil changes, which led to sludge buildup, including on the rings, leading to sticking rings and high oil consumption. There was a TSB on the topic, but I think your year is well out of range.

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Prost!

THis is a possiblity, but I would go the extra mile and have a leak down test get to the bottom of your problem..then you will truly know what is causing your low compression..hopefully the news will be good.
Bob