When I rebuilt the rear axle on my W109, the nylon bushings on the brake bearings where worn and the axle tube had some slight pitting. I cleaned up the axle tubes with some very fine emory cloth and installed new nylon bushings. That was over a year ago and I not had any noise or chatter when braking in reverse. After 40+ years most W109 cars will need to have these bearings replaced due to wear and lack of proper greasing. There are grease nipples on each bearing that are very easy to miss. This job can be done without having to remove the entire rear axle from the car.

If you do decide to replace the nylon bushings yourself you'll need 2 of these repair kits from mercedes 1094200078. This kit includes new nylon bearing shells, two rubber seal rings and two felt seal rings

You'll have to remove the brake caliper, rotor and backing plate to get access to the bearings. There are 4 bolts holding the bearings together and at least one more large bolt holding the bearing to the brake support arm. One word of caution. The rubber seal rings that seal the bearings will probably have to be replaced. To be able to fit the new rubber rings over the axle housing, you have to pull the axles out. The upside to pulling the axles out is that you can clean and repack the rear wheel bearings and replace the inner and outer wheel bearing seals. There is a repair kit available from benz that has both seals, gaskets, and bearing lock ring 1113500068. Also the big blue mercedes shop manual for W108, W109, W111, and W113 cars has all of the detailed information about replacing the bearing shells and R&R of the rear axles.

From my experience I wouldn't say this job is impossible, but time consuming and very rewarding when fixed properly.

John