12-12.2 seems a bit low (maybe). Also the bendix gear has to pushed by the solenoid rod into the flywheel teeth pretty much before the main starter is energized. Might be an issue there or a juice problem. Did we try another battery? recent problem? I'd loosen the starter & have a helper work the key as you jiggle/move the starter. Is there an inspection plate if removed will let you see if the teeth are coming all the way forward to mesh & you can take off the main cable & jump the solenoid only to kick it forward & see how it is going (if you can visually see them mesh on a stick, I dont know sticks)