If the stopper mod had been done there would have been a short length of studding or rod, around 11mm long, under the rubber head of the plunger.
Drive out the roll pin (a pop rivet stem works well) and lift off the head. Invert the cct and if a section of rod drops out, it has a stopper fitted.
You don't need to remove the internal body circlip and worm drive.
It's not falling off, it's an upgrade opportunity.