A good test may be to check the end clearance with a dial gauge before removing and repacking the bearings. I suspect the surface hardness of the bearings when starting to wear is worn through easily.. So if you have too much end clearance the bearing and or races have wear. How much is too much? Only people that do the test may define that over time. No signifigant increased end play they can be repacked.

Although it seems funny if most brands of bearings do the same on these cars.

I would not repack and instead change these bearings with the presence of much additional end play. Also maybe the problem will go away with another brand of bearings.

Since cost is not an issue I doubt I would use the brand that was originally sourced by Mercedes as well.

All this said I must make it clear that I have never had a hub off one of these cars. I have just heard their bearings are troublesome.