I don't know a lot about Mercedes Bearings, but I've been working with bearings in everything from 2 stroke racing bikes through to wheel bearings on other automobiles.
I could not think of a good reason why you would need to tighten a bearing to fix it. Other than the obvious bolt backing off.
For the cost, importance, and huge wear that bearing get I would think no brainer to replace?
Not sure why people say to tighten them, I actually heard a mechanic say this "tightening bearings" just the other day in his shop to a client.
Seems more like a quick, gonna sell this car to someone else, fix.