I had the same disk looseness problem on one of my 2.10s. It was brand new. It would rotate on its own. I talked to Gerard Enterprises, the US importer and outfit responsible for warranty work, and was told to try to put thin CA in the bottom of the O-ring grooves. Tried it but the disk was still loose. Finally sent it in to have them look at it. I was told everything was within spec. Not sure how everything can be within specs but yet the disk still rotate on ite own. They put more CA in the bottom of the grooves. Now the disk is so tight I have to use pliers to turn it. Thye said it would probably loosen over time. If you haven't always had the problem of the disk being loose new O-rings will probably take care of the problem. As others have said, you want to make sure to use the correct replacements.

Dan