I have a problem with sticky grippers on my SP-15. Everything was working fine, then they became stiffer and stiffer until they didn’t want to open at all. As far as I can tell the foot pedal assembly is fine. I’ve taken apart the gripper assembly, cleaned and lubricated it. While it seems to work now, it doesn’t work as smoothly as it should. I’ve been using AGS powdered white lubricant in lieu of graphite. Are there any other lubricants I should use? Or any other reasons why this is happening? Thanks so much!