Jinman, thanks for your' advice. Tried hard to buy the cylinder from the local dealer but after an unanswered email and two non-returned phone calls I gave up on them. Bush Mechanic time ! Cut 2 30mm long pieces of 12mm copper water pipe and split them lengthwise. Prised the split open enough to slip over the shaft of the leaking hydraulic cylinder. Squeezed the first one closed with pliers and put the second one on top of the first with the split opposite (ie 2 thicknesses of copper pipe). Put two small diameter worm drive hose clamps on to keep everything tightly closed. Finally, jammed a squishy rubber ball down behind the steering column where it' lodges against metal, not fiberglass. Have since mowed 18 acres of very high grass with no problems and the column still lifts up to allow ingress/egress. The 30mm length is perfect wheel position for me but everyone is different.