The thing is Ian, that your rack shouldn't rotate. I'm aware that 08/09 Roadsters look different around the rack mounts to my 2005.
In fact I intend to do some research over the Centenary week and get some pics to establish just what's changed with respect to the steering arms/track rods.We know these were upgraded and the bump steer was reduced.
Anyway, here's a photo of my nearside rack mounting:
And here is the same mounting from below:
The rack sits in a split alloy block. I haven't had this apart, so I don't know whether it works like a pinch bolt. The engineering solution would be to have a dowel or cotter arrangement inside the block for accurate location. Maybe it's like that, but if yours rotates, then I wonder.......
The offside is here........and the pinion housing is visible lower left.
What you need to do is look closely at the alloy blocks (if yours is the same)and see if you can twist the rack by hand. (Probably not). Check those bolts for tightness. I would be inclined to take the bolts out (one side at a time) and apply some 'Locktite bearing seal' which is heavier duty than thread seal around the rack. Reassemble - do the other side, and leave it overnight to dry. If that doesnt work there are two more solutions. First is to take some metal off the U block 'legs'using coarse wetndry on a flat surface (sheet of glass will do)so that the clearance is reduced and you get a tighter grip. The final option is to lightly drill the rack housing, drill the U block to match, and fit a small ball bearing, which might just do the trick. That's a last resort though.
Good Luck.
