Dexta lift works until the tractor gets to operating temp.

[delta bob]

When the tractor gets warm the lift stops working, any ideas?
 

[Randyr]

Sounds like the pump is worn.
What oil is in it?
If it's modern TDH oil, it's too thin. Many people report trouble with their hydro lifts on old tractors with that oil in.
If you do have TDH, try going to a GL1 80w90. Don't use anything other than GL1 because the others have EP additives that are harmful to the brass/bronze parts in the tranny.
An alternative that many are doing is to use 15w40 or 10w40 motor oil. There are many posts about it, and it's worked well for everyone.
If you are already using the thicker oil, then sorry your pump is worn out and needs rebuilt or replaced.