This seems to be restriced to the m112 v-6 gas engine balancers.
I have seen one m113 v-8 do it. I have never heard or seen a
AMG one do it. No diesels or 4cyl/12cyl either.
There was a problem back in 99/00' with AMG crank pulley being
machined out of round. This was causing the front crank seals
to leak.
The seperating balancers are more common now,
We see these all the time on all models with the 112 v-6.
I am replacing a timing cover and oil pan on a 98' CLK 320 at
this very moment because the balancer came apart.

If your dealer says "Not a known problem", they are full of it.
If your car is out of warranty, the area market manager can decide to goodwill the repair.
Make noise. Call the MB Client Assistance Center and make noise.
1-800-for-mercedes. We have seen about 1 a month.
Most have been 98's.
Good luck to all.
DR.D