Air valve spring


Air-Valve Autobot!
Today I extend the air valve spring of my IWATA CR REVOLUTION because it start to not return very often and is very annoying , at first I thought that need some cleaning but was not dirty , maybe the o-ring is starting to degrade ?
I buy this airbrush just 6 months ago and never use uretanes or solvents ... , is a common issue ?
I've never heard of a air spring going soft especially so soon. Is the inside of the valve also clean, not just plunger?
The lunger looks brand new , as the rest of pieces , I feel like the o-ring turn too tight around the air valve piston , work well now but is getting numb again