IMO the most likely suspect is the driveshaft front flex coupling. If you get the car in the air you should be able to get under there with a flashlight and check it for cracks. With the transmission in park twist the driveshaft back and forth and you should be able to see any cracks in the rubber.
This part is the same or of common design architecture on the 201 and 124 models and they are usually shot by 50-60K miles. It acts as a torsional damper, but is not very durable. When it cracks the drivetrain feels like a rubber band and the excess torsional play causes clunking sounds because the damping function is lost. I discovered mine was cracked when I did the 60K mile service. Since I had a service coupon from the dealer for an hour's free labor, I had them do the swap, so my only cost was the part.
When I got the car back I inspected their work and found that they did not index the front and rear driveshaft sections properly, so I took it back and had them fix it. Upon reinspection, they got it right.