The off-face condition has to do with wear to the hook and hinge pin (movement in the fore-aft direction). If you can close the gun on paper with the forearm off, there is wear. If you can close it (with light force) on two thicknesses, you probably need to have it put back on face (new/built-up hinge pin, built-up/shimmmed hook, or some of each - not unduly expensive). The locking bolt should preclude any rotation around the hinge pin (opening movement). If you can feel any up-down looseness, the bolt and locking slots may need attention. I'm not exactly sure which of the Parker parts inter-relate, but sometimes bolt spring pressure and forearm pressures will mask an off-face condition.
