It appears the problem with the 1200 GS bikes is the splined flange mounting system of the rear wheel .
I enclose some literature about the BMW fix for this problem .

© 2004, BMW of North America, LLC
BMWMotorrad
USA
Service Information Bulletin
Subject: Bearing play at the rear wheel drive
Model:
Details:
Aftersales
Solution:
Dealer Operation/
General Manager
Sales-
Motorcycles
Sales -
Used Motorcycles
Business Manager
(F&I)
Service Parts & Accessories Administration
Date: February 2005
Bulletin #33 001 05 (011)
Source: 33 74/2004
BMW Motorrad USA Service and Technical
Contact: Respective Aftersales Business Consultant
R 1200 GS
1: In the rear drive of the R 1200 GS the ring gear is supported by two types of bearings:
one floating bearing and one fixed bearing without preload. Inherent in this design
is a small amount of bearing play at the rear wheel. With all components manufactured
and assembled to stated tolerances it is possible that play in these bearings can be felt
and measured at the rear wheel. This type of bearing play has no effect on motorcycle
handling or on the durability of the bearings.
2: There is a possibility of play developing between the splined wheel flange (P/N 33 17
7 668 659) and the axle tube of some motorcycles manufactured prior to 08/2004, US
VIN# ZL 76187.
1: In the event of a customer complaint, an inspection and measurement of rear wheel
bearing play is to be performed as described below. With cold components the total
play (back and forth travel) allowable at the wheel rim edge is 1mm(maximum). Refer to
the R 1200 GS Repair Manual CD for measuring procedures as well as temperature definition
of "cold components". Replace the entire rear-wheel drive assembly if the play
exceeds specifications.
2: If the complaint is "bearing play at the rear wheel" you must first check that the
splined flange is secure before performing the measurement noted in point #1. When
rocking the rear wheel back and forth, you must first make sure there is no movement
between the wheel flange, the rear wheel and the axle tube.
If play is noticeable between these components you must replace the entire rear wheel
drive assembly (complete with flange). Replacing the splined wheel flange only will not
solve the situation, because in all probability the splines on the axle tube will have suffered
some degree of wear as well. If you are in doubt, you are requested to contact your
respective Aftersales Business Consultant.
Warranty: Covered under the terms of the New Motorcycle Limited Warranty.
Important Note: Screw 1 is a drain
plug for repair-related oil changes; it is
not for checking the oil level. When filling
the rear drive assembly with oil,
pour in the defined quantity (0.25 l for
initial fill, or 0.23 l for oil changes)
through the bore for the ABS sensor.
We highly recommend using BMW
Super Synthetic Gear oil. 75W 90, P/N
07 51 0 394 082

I read this info on the ADVrider site and have included it for anyone that might be interested .Anecdotal evidence suggests that bikes leaving the factory can have as much as 1/4 inch of play at the wheel rim .

It seems that BMW have tried to fix the FD problem by adopting a splined flange mounting for the rear wheel but build quality was not of a sufficiently high standard .The result is that an initial sloppy fit or poor quality materials induces even more wear as the bike racks up the mileage .
It might be advantageous for owners of bikes made prior to 8/04 to check their rear ends and have them replaced under warranty .

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