I am interested in this problem because it is an interesting metallurgy failure -rather like the piston ring problem on 2005 SLK350's.I am hoping others will chime in to correct/add to what I found.
You can find lots of info if you google "M272 balance shaft failure" .It will also give info on a Class Action suit related to this. Interesting that the V8 M273 engine which has the same sprocket but not the balance shaft(V8's are inherently well balanced unlike our wobbly 90 degree V6).
The symptoms of this sprocket problem are initially "valve train clatter" .Eventually a MIL code is set- 1208 or 1210.Sometimes the problem is misdiagnosed and the culprit is the purge valve chattering.
The best source I found was:
MB DTB S-B-03.03/08i dated October 24 2008. -lots of tech details and photos.
Repair kit part number is :repair kit is A2720300013 w/o replacement of oil pump.Repair involves more than simply replacing one sprocket!
Repair takes over 30 hours because engine needs to be removed and front of engine stripped.
The cause was 'soft metal' (actually a failure to correctly heat treat powdered metal) being used for "SOME of" the balance shaft sprocket on earlier M272 engines.
M276 engines do not have the balance shaft because they are inherently balanced 60 degree v6 (not unbalanced 90 degree V6 like M272)
The problem can affect all M272 enginesup to engine number
272.942) 30468993. The last 8 digits are what matter .Those I put in parenthesis merely identify the engine type/application.This means if you have an '07 or earlier,you'd better check your engine number.The number is on the front of the left cam cover but is difficult to find read. Your MB dealer can tell you the engine number from your VIN.
Although there are some press reports of goodwill repairs,most enthusiast forum contributors dispute that.
Mercedes Hit With Timing Chain Issues on 2004-2006 V6 and V8 Models | The Truth About Cars
Mercedes seem to have been late to learn the lessons of GM's ill-fated 90 degree V6 engines(according to some).Such sources would cite the change to 60 degrees for the current V6(M276) which is a chrysler developed design:
"Mercedes did something absolutely masterful, and only those who pay close attention realize that something changed from the 90 degree M272 V6 to the 60 degree M276 V6. The M276 V6 is Pentastar derived and other than the fact that the V angle changed which MB does document they make no mention of the change, and in fact to most it appears to be a direct injection version of the previous V6. "
BMW are planning a new 90 degree V6?
The Spun Bearing: The Case For the 90 Degree V6 (With Reservations)
I hope others will correct factual errors and add to the information to help those with balance shaft sprocket failure.