This is super easy to fix. I purchased an old kiln last year with the same problem. It will only take you 3 minutes. Unscrew the face plate of the plunger. Then take a screw driver and just wiggle the piece inside that holds the plunger in place. The manufacturer stresses not to use any oil of any kind. My was rusted in place and would not move to hold the plunger. After wiggling it back and forth a couple times it worked flawlessly.