the hyd cam lobe has sideways slant to it so it rotates the lifter so they don't wear out, you can use solid but they do not seat flat on lobe
Solid and hydraulic cams both have an angle ground into the cam face along with a slight dome on the lifter face to keep the lifter rotating. If the lifter stops rotating it is instant disaster.
Clean it, if it's Dirty. Oil it, if it Squeaks.
But: Don't fix it, if it Works!
