Wheel bearings in 124/201 cars generally last the life of the car unless it seen a lot of water, snow, etc. 300-400Kmi is not unusual. The bearing is sealed and non-servicable. Replacement starts with removal of the axle halfshaft. Then the hub flange must be removed with the use of a 10 lb slide hammer. Can come right off or take 30 minutes of pounding. Then there is the press used to install the new bearing. Some have made do with creative use of custom tools, many just pay labor. Are you really sure the bearings is worn out? I had a very bad thumping in the rear that turned out to be in part caused by a bad tire.