ford cargo 813 power steering noise?

My ford cargo 813 H reg power steeringmakes a grinding noise and judders only when i put the right hand lock on/turn right.have check fluid level that seems fine.have look for leaks from pipe but they seem fine.the only place that i could see oil/fluid was out of the top through the cap as its has splash onto the side of the compressor.any ideas would be helpfull