My second 16mm projector, a B & H 624 has a little problem with the focus. The projector's slight vibration seems to make the focus slide just a bit out of focus. Ever 4-5 minutes I find myself make small adjustments to the focus. That has never happened to me for the Elmo 16CL or my Eumig 810 D. Have any of you experienced that, and do you have any suggestions? Not sure what kind of anti-lubrication I should use to the mecahnism.