If the locking collar is engaged and you have the locking screw loosened, it could be worth trying to release it first. (Screw anticlockwise) I just tried mine and when the collar is engaged it can be quite tight to then disengage. Try it with your spare, engaging and disengaging the locking collar does not affect the calibration.
Re lubricant the internet suggests clock oil for micrometers. (not silicone which creeps and could end up on the optics)