Thanks Richard & Steve for your posts. They answer my questions, and I suspect for many others.
I'm not a club member yet, owning Heralds and looking after my daughter's Standard Companion membership of clubs is getting expensive.
As to what I have fitted to my car going from my previous post on Trackerjack brakes/brakes I don't know. You will see what I thought of the car's previous owner (thanks for your help on that subject Steve, sorted). What he did with the car has probably caused issues with the brake master, it is weeping slightly between the reservoir and piston unit from being knocked doing other correction jobs. He also said he had issues with the fluid warning light so he disconnected it, I now know why. My problem occurred with the clutch master because I ordered the correct seal repair kit only to find the master was a 3/4" version, not 5/8" (previous owner or Mr Leyland altering the spec?).
Incidentally, I had previous issues with the cast iron clutch slave, that was sorted by re-sealing but when the master went I ordered new cylinders for both ends. I haven't fitted the slave (it wasn't leaking when I took the line out of the car) but the slave I got came from MGB Hive, it's identical in terms of fitting, bore etc to the Dolomite, the unions are also the same, just rotated by about 45' so thanks RobSun for the pointers. I also took the opportunity to do a permanent job on the pipe, making it all copper with an Omega loop in, as per Heralds.
I did wonder about there being multiple variations on the masters, it didn't make much sense, Mr Leyland doesn't help with the 1979 parts catalogue, nor do Rimmers because I would have ordered the 1300/1500 version, now it will be a wait and see until I get the old cylinder off, or more likely go down the club route of the S/S version. Either way, the cylinder fitted to the Dolomite is crap compared to the tandem version fitted to the Spitfire, the reservoir is pinned to the piston section, I have a new one I intend to fit on my Herald estate (possibly USA influenced for safety?)
Richard did highlight a potential problem of bleeding the system I hadn't thought of. Now it will be, fill the reservoir to the top, open both lines and a few good thumps on the pedal.
Thanks again to both of you.
Don't slam the pedal when bleeding against an empty system, you can damage the Bakelite bit in the servo which is NLA.
Its OK to just open the taps on the master to bleed it, gravity will do the rest! The PDWA really does cause a lot of problems bleeding the brakes on late cars. Lately I have a tendency to throw them away as they don't do anything useful and use the wiring to power a level sensor cap on the master which does! Not a 5 minute job to delete the PDWA though as you need 3 new metal pipes plus a 3 way and inline joiner.