I have a gold filter but under a different brand called "Xin Yong Shi" . The dimension of the green O ring is 2.5 mm section x 38 mm OD. The Oring has a snug fit with the seat at the end of the aluminium tube so you just need to measure the diameter of the seat with a caliper to determine the OD.
The material of the O ring is a bit soft and everytime I open up the filter, I saw fine filaments of O ring material spread around the seat. I believe it was caused by the O ring being cut when the high pressure squeezes it into the gap to be sealed . However, there has not been any failure or leakage after a year and I still have got two spares that came with the filter so I think it will be good for quite some time to come.