I have an older (yellow) Case 970 w powershift. Put a new relief valve in a couple years ago and had trouble with hyd system this year. Replaced all the oil at that time. Oil gets hot and will not lift either cylinder or 3 pt arms with a load. Cold, it is fine, hyd oil temp went almost to red zone and even had trouble with powershift going in reverse. My mechanic also has two older Cases doing the same thing and can not figure out what is wrong. Did isolate a problem with using a single action cylinder. Tractor is worthless without hyd and 3 pt for me. It is not used much except for spring and fall. Maybe 50 hrs for the year. Any ideas? All filters are changed each year.