Update as of 7 PM EST
I am not longer getting the drip now however, still would like to know where the O-Ring goes. I ordered a replacement since it was missing.
I am very frustrated when trying to replace my old cartridge which is a Unicel C-8409 with the same Unicel C-8409. It seems the newer ones (and I've tried two of them) don't fit? When I'm turning the pump to a lock position, it sounds like I am scraping plastic as I am tightening it to the very end. So I ordered a Pleatco PA-90 Microband and that seems to fit better. However, I've noticed on the Unicel and Pleatco that I am getting a drip from the top part of the pump. It's dripping right near the Sta-Rite Locking Mechanism and causing a puddle of water at the bottom of the pump. After further examination, I ordered an O-Ring because that looks like it's missing, but I honestly have no idea where it's suppose to go? I don't even know if that's why I'm getting a drip or if the filter still doesn't fit but if anyone has any pictures of where the O-Ring goes, that would be great and I'll try that first.
BTW, I am 99% confident I have a Sta-Rite PXC-95 because the C-8409 has always been the cartridge when replacing, but the label in the back has 3 models. PXC-75, PXC-95 and something else which is also frustrating so....
Thank you for your help.