[Derek UK]

I have a Girling servo that was fully rebuilt by Norton, it's not been fitted, they state explicitly that silicone fluid is not to be used with it so I won't. Some seals like a bit of friction to enable them to flex and seal and I think silicone fluid can be just too slippy in some applications.

The Lockheed servo on your estate would have been fitted after it was sold. Estates with discs, i.e. later ones, had a Girling servo as standard the same as the GT.You infer that the servos have been sitting around a bit and maybe they are just sicking due to condensation induced corrosion. Yes the Girling servo is notoriously fussy about rebuilds. As Peter says, alignment is critical and repair kits had, maybe sorted now, parts that were the wrong size. Diaphragm maybe? Also easy to get the small valve pieces the wrong way round.