So you got a great deal on a used Aeron, you probably paid between 200-400 dollars, locally. The cheaper you paid the more likely, it didn’t have a lumbar, or the foam cushion. More likely they left the same casters from 20 years ago and maybe the arm pads have deep scratches. At first glance you don’t mind, because you feel like, you got the deal of a lifetime for one of America most sought after chairs. 
And now you see my ad, you start looking and realize your chair could be better, new arm pads, a lumbar, casters, & maybe even the foam cushion you never knew they had. I can even assist you in removing and installing the Aeron parts. 
Casters will be hardwood floor casters and may vary depending on availability. But they will fit the classic Aeron Chairs.
You can also upgrade from a lumbar to a Posturefit (Y-back) back support, also brand new. 
Message me for more details.