I have a late model 770 with a loader .Several years ago I added a remote valve and tapped into the hydraulics power beyond port . I also added a remote reservoir because loader would drain the system when raised very high.I have always had a problem with the tractor overflowing the hydraulic oil after lowering the highlift ,or shutting off the tractor .Last winter I decided to take a look at the pump to see if anything looks abnormal.There was very slight wear on the end plates . But there was some scoring on the ends of the gears and the center  plate.I decided to live with the problem and put everything back together . Now I a problem with oil foaming and very slow lift on loader arms .and the oil foams and overflows a lot more than ever  I have the pump out again and everything looks like it did before.Any ideas would be great   Ray