Mine went stiff, had same question.
The answer was to pull it off and wipe the inside with a dry oily cleaning cloth.
We were told vaseline but so far I've not needed to use it.
Shiny Blue EV2 Mk2, Falcon T50 10-50×60
John Bowkett BSA Goldstar SE RNRR, Bowkett Carbon Shroud/moderator/air stripper, Aluminium scope riser made by Shawn, Polished trugger guard snd am soon to fit cheek piece risers. Hawke Airmax 30 AMX 8-32×50