Seeing as the brake system is entirely removed from the car for re-piping and re-rubbering, this seems an opportune moment to have a look at the mysteries of the "G" valve.
This MkII one is really a very simple machine. Hydraulic inlet at one end, rolling ball in the middle, rubber seal and tube at the hydraulic outlet end. Hit the brakes hard enough, the ball will roll up hill and go splat against the seal, thus cutting off further flow to the rear cylinders.
Remove the big nut on the end. I used a 36mm impact socket and the air ratchet.
Spacer down the bore - ball behind.
A sharp tap rolls out the ball and the spacer. Down at the bottom of that dark hole is a rubber seal and a little spigot tube. I have made a number of attempts to photograph it and that's the best one. Sorry.
So, out with the Girling SP2275/2 seal kit.
You need these three for this valve. Big one is the seal for the cap, spigot goes into the bottom of the chamber and the seal pushes over it. Cleaned everything, applied a goodly dollop of rubber grease and re-fitted the cap.
Here it is back in the engine bay with a freshly painted bracket.
I hope that's clear enough - best I could do with the pictures.