Try Lucky Motors on Druid Street, just south of Tower Bridge in East London.
They have just replaced all 3 seals (drive from gearbox and drive to both rear wheels) on my rear differential (big job), changed the rear brake pads, plus new diff oil, plus bled the brake system for £430 all in.
The work is of high quality (I have watched them work on my car) and I think they are miles better (more thorough, and a lot less hectic) than George Fraser where I used to go.
Call Lucky on 07932 900411 or 020 7357 6405, tell him Sean (chinese guy) from Wapping sent you.