Vauxhall don't sell the rings seperately but you can get them from ebay.
You have to remove the drive shaft from the back of the wheel, knock/split the old ring off, heat the new ring with a gas torch to expand it then quickly slide it on to the shaft, making sure you get it into the correct position.
However, a new shaft complete with ring will not cost much more if you shop around.
rupe, January 2012
