Hi, I realize this is coming about 2 months too late, but I had the same problem. I just tried out this:

https://smile.amazon.com/gp/aw/d/B0051XY42Q?psc=1&ref=ppx_pop_mob_b_asin_title

and it works. If the link doesn't work, it is an o-ring with the following dimensions:

0.5 inch inner diameter (ID)

3/4 inch outer diameter (OD)

1/8 inch width

The particular one that I ordered was the 206 Buna-N O-ring, 70A durometer, round, black. It feels sturdier than the o rings that come with the chair too.