remote brake servo

i am in the process of stripping a lockheed remote servo i have removed the retaining ring around the servo part but i am unable to remove the remote master cylinder inside is a large rubber seal and a large black plastic round ring i need to remove these to get to the nuts holding the master cylinder on how do i do this! i cant see any retaing pins in either of the two brake pipe unions or down the pressure equalisation tube the normal places the rubber seal and plastic ring do rotate but dont seem to unscrew
any ideas /ubbthreads/images/graemlins/confused.gif

Chris, if you take off the rubber seal first, in the groove of the plastic dome where it sat is a slot. There is a locking plate in the slot that needs to come out. Position the slot downwards to let gravity do its work. Gently push the plastic dome, and the locking plate should fall out.
regards
Dave

so simple yet it baffled me thanks dave
chris parker