I have just copied the explanation from ebbo's link - it describes the type of bearing - I have no reason to disbelieve it!
Start of quote.
"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"
End of quote