I have a 4x5 Cambo, the one with the square rail and round standard uprights (it's a lower end model). I've had it for about 30 years, with no problems. There are two knobs each to move and lock the front and rear standards, one tightens and one moves the standard. Lately, the rear standard tightening knob is harder to turn, like it is dirty, but it also tries to move the standard while tightening it, so it's difficult to tighten the standard after finding the right position. It still tightens, but it also will move the standard while doing so, unless I hold the moving knob just right while tightening. There is some play in it also. Anyone know what I should do? Seems like something I can do myself, but I wouldn't want to clean or lube with the wrong stuff.