I had wrote up a very detailed explanation of the problem and how to solve it but some how i lost the whole post so... Simple solution is to remove your rear brake pads and file away the sharp leadign edge and reinsert them.
Hope this helps, cheers
Just for anyone that wants to know, i changed my gearbox and diff oil yesterday and refilled both with Redline Shockproof Lightweight Oil and it appears to have done the job perfectly for gearbox and diff. hope this helps