Thanks for the replies, perhaps I should have been more explicit.
This is for a car that's been off the road for about 30 years and the brake/clutch parts were removed maybe 10 - 20 years ago. It's a long ongoing, body off, restoration project and I'm at the point now, having earlier this year got the engine running again, of sorting the hydraulics (new pipes/seals etc ). I've already, some years ago, replaced the clutch master cylinder as the casting was cracked around the pipe union thread.
I could of course replace the brake MS but as it's in very good condition, apart from the holed plunger (which fundamentally stops it working ... the fluid would leak out :-) there's no reason not to keep it, unless I can't source a placement plunger, which it may turn out I can't . If new ones aren't around then a used, unfixable MS (e.g damaged casing) would solve the problem as a source of the plunger.
There's no hurry for this, the cars not going anywhere near a road for some time.
Chris