Right time for an update. Got my bike back today; 22 days later. All fixed under warranty. In addition to new drive shaft and final drive, it looks to me like the final drive casing and rubber gaiters at both ends have also been replaced.
In response to GrinningGSer: As far as I can make out, a splined shaft exits the sealed final drive. The prop shaft mates with this with a female splined orifice. This splined set up was stripped on both components. As I have found out since my original post, the drive shaft casing runs dry, hence the rubber seals at both ends to keep water out. It was water ingress which caused the corrosion.
I suspect my drive shaft had quite a bit of water in it, and as there are no drain holes, it had nowhere to go and caused material corrosion which in turn caused the mechanical failure.
A rear wheel drive car has a prop shaft, which mates to the differential via a similar splined arrangement. This is exposed to the elements and should be greased. When it gets wet, the water drains off / dries off as it is not encased. A far better solution.
So to me the GS drive shaft casing has a fatal design problem as
a) there are no water drain holes
b) there is no grease point