Rh90c e

We have Bucyrus RH90C E, and we have problem with the bucket cylinders. When the cylinders are fully Retracted and when controls are in neutral, cylinders bucket begin to extend on one portion of his stroke. We checked servo sistem and relief valve. we have 300 bar on both sides of cylinder on max hp. When it freely move, pressure in work line decreases on 0 bar to its stop point, when it stoped pressure begin to increases to ~12 bar. We suspect on cylinders,

If someone knows another option ?!?!?

Rh90c e