Booster brake bleeder

[Coron]

Hello All
I have just rebuilt my Benaldi Duel master, installed it back into the car and started bleeding the brakes, got through the rear two calipers and went refill the resovour again and noticed a 10mm bleed valve on the booster closest to the front if the car, loosened it and bled the booster but when i went to retighten the bleed nipple it wouldnt budge then "snap" the nipple broke off half in my spanner and the other half is 1mm above the PBR booster casting.
the offending booster is a PBR and the other working booster on the car is a Benaldi.

My question is, is the PBR booster standard? if not does the origional have a bleed valve at the booster or is it bled through the rest of the system?

Thanks guys

Harry