As a replacement for a defective scope, Crosman sent me one that you can dial in the yardard by turning the focal mechanism on the front of the scope. It ranges from 5 yards to infinity. Only problem is that it is very tight and hard to dial in the lower distances. Tried putting it to 5 yards and pulled the scope off the dovetail rails. Is it OK to lubricate the distance dial and, if so, with what and how much? Thanks.