With my 300 (not 300x or 300cx, but I 'think' the mast to bracket connection is the same) I think the issue is wear on the 'pocket', be it the loader side or mount side. I keep the adjustment bolts and jam nuts/bolts tight. To get them tight, I lift the front wheels off the ground with the loader, then tighten the adjustment bolts out TIGHT, and the jam nut, and set screw bolt. That takes as much slack out as possible. However, having done that about once a year, I've notice the loader doesnt lower to the ground as far as it did when new. Which stands to reason if you study the geometry of the loader frame, mast, and how wear of the pocket and tightening the adjustment bolts to compensate, changes the final available down travel of the loader. A bolted solid connection and bolted brace from mast to loader frame/hoop that attaches to the front mount, may also be in order. Ive lost 2" of down travel, getting it back would be nice. Ive also thought of shims inside the pocket to compensate for wear, would allow loader more down travel.