I just wanted to say thanks for all the info {especially from EFC} I went to see Justin Sutton at Sutton Tractors and they explained my problem as being in the valve.
Rather than trailer my tractor 120 miles I just took them the valve, they gave me a new valve and a lot of good advice.
Some really nice folks at Sutton Tractors by the way.
I hope to have it installed this weekend.
I also learned a lot about my little Iseki from them ,like where the hydraulic screen is hidden...
again, thanks everyone for the help
David