This very good looking and seemingly flawless copy of a valve plate for a Rexroth A6VM series motor is, actually, a useless piece of scrap - the curvature of the valve plate is not equal to that of the end plate!
To reveal the difference I marked the sealing surface and then rubbed the plate against the end plate. As you can see, the only contact points are the extremities of the valve plate. Further measurements showed that the gap in the middle of the valve plate is 0.3 mm wide - meaning - "rivers" of internal leakage!
It's easy to feel the part is bad by moving it in its place - it "feels funny", the drag is ubnormally light. However, due to the fact that this valve-plate is so well finished, a less experienced mechanic could easily mount it without noticing that the part is faulty.