The leg locking mechanism is not meant to be removed. Once it has been removed, it no longer stays in place and allows the leg to be locked. I have an older Marchioni Bros as well, and that is one of its maladies, I bought it from someone who failed to mention it. Now I have a leg that wont stay extended. Fortunatly, its one of the lower joints, and doesn't matter too much(unless I need to go tall). I think the part is a press fit, I may try a spot of JB weld to attempt a repair. The ring you are trying to remove, should be visable once the outer knurled ring is unscrewed. Try pulling the leg out of the outer (larger) leg joint.The ring is most likely inside the knurled locking ring, and will come out once you get it past the smaller section.