Just recently my FMD 3 point hitch arms are slowly leaking down when tractor sits in shed. Unloaded Arms will drop approx. 6 inches in a week of sitting . When I bought this tractor 21 years ago the 3 point arms would,nt lift at all. I found a deteriorated lift piston sealing ring. Replaced it and the hydraulics worked perfectly till just now. No leak down at all. She would keep the bush cutter in the up positions all winter long , just sitting parked in her shop. Can anyone shed light on this problem. Can it be that the same seal is leaking slightly or can there be some other issue. I welcome any input.