I agree with Jeff - replacement is the way to go. But I would make sure that this is the real problem first.
The front bearings look to be a reasonable DIY, judging from the Haynes book. The rears are not even in it.
Looking at my Merecedes 123 chassis manual, R/R of the rear wheel bearings takes at least five special MB tools and appears quite complicated. Better to leave this one to a shop.