You do not indicate what model MB you are working on.

I will assume that it is a 123 diesel since it is the most common engine to experience this maledy. What I will say probably applies to whatever model.

The most common problem with these harmonic balancers occurs due to ignorance on the part of mechanics that have removed/installed harmonic balancers on other make cars and follow the same procedure on these engines. That procedure potential can destroy a crankshaft on these engines.

Many cars have a square keyway on the crankshaft snout that matches with a square keyway on the balancer. The square keyway type is super simple to put together. You start the key in place, put on the bolt and walk it into position with the bolt.

MB engines, at least the 123diesels, have two dowel pins that match up half of each hole in the crank snout with the other half of the hole in the balancer. What commonly happens is that some gorilla comes along, looks at the pins, lines them up by eye, starts the bolt and walks (forces) the bolt down to pull the balancer into position, probably with an impact wrench. In the course of turning the bolt, however, the balancer rotates slightly resulting in misaligned holes. The parts are all a little soft, so when the bolt pulls everything snug and out of position if they torque down hard, the bolt will pull it mostly into place.

This Jake Leg procedure usually results in a broken crankshaft snout, balancer coming loose or both.

The CORRECT procedure is to take the adequate time and trial and error approach to put the balancer in place slightly counter clockwise from its ideal position, so that the rotation of the bolt slipping on the balancer turns it slightly into proper alignment.

This is NOT a job for an impact wrench. If you see someone getting NEAR that bolt with an impact wrench, tell them to STOP, and sweep together your pieces and find someone with an IQ above 75 to complete the job.

In your case, you MUST use a harmonic balancer and remove the balancer to assess the condition. If there is any crankshaft snout remaining, make sure the dowels are okay and take the necessary time to put it together correctly or I can guarantee that you will eventually be very sorry.

Best of luck,