This monitor has no OSD or button to trigger a degauss. The coil will be wired directly to AC via a posistor, so it's entirely passive and will only trigger again when the monitor cools down.
The distortion is caused by the high voltage arcing over, which droops and interrupts beam deflection for a moment. I wouldn't want to run it this way for very long, because it can damage the flyback transformer over time (although the flyback could itself be arcing anyway).
Ragebutt's advice is good RE: maintenance. I would take the back off, make sure it's discharged then clean around the anode cap and in general make sure there is not excessive dust/soot that could form a path for electrical discharge. Clean the anode with alcohol, apply a little dialectric grease to the cup and put everything back together. There is a decent chance that will help, just make sure not to wipe off the black paint on the tube - this is called "aquadag" and it is important to the operation of the monitor.