CAT 416 Backhoe. The bucket lift suddenly became very weak and would hardly lift half way up. Working another control would seem to make the bucket lift momentarily. All the other hydraulics still worked flawlessly. The problem turned out being the o-ring seals on the check valves in the hydraulic valve group. There appeared to be a redesign of the check valve assembly with the new design having backing rings for the o-ring seals which makes my think this was a common failure mode. In my internet research on the the symptoms I was having others have reported the same problems and said that this problem is the result of the pump not being triggered because a blown out seal in an adjacent control valve in the control group. In most cased the check valve for the valve for the control that is not working is not the issue but another one in the control network.