Thanks for all your info Born - tried all your tips to no avail. In the end I brought a recon'd rear master cylinder from ebay for £12 - back break is bloody perfect now.
(The tell tale sign for me was the lack of a little woosh of fluid into the reservoir when the pedal was depressed)
(The tell tale sign for me was the lack of a little woosh of fluid into the reservoir when the pedal was depressed)