Mike,
Who have you got to do your mastercylinder? I want to get one done too and wondered how much do they charge and does whoever you are using supply/fit new piston/seals? (I believe getting the circlip out is a bitch of a job without correct superlong pliers).
I got a brand new repo 5/8 th m/c from Tony Huck @ Maitland Racing for £45, looks same a original one, a seal repair kit cost more than that!!!. Buzzard.
Every man should have a shed (for bikes obviously..)