My bother has a new holland L555 we have flushed the hydraulic system 2 times because when he bought it, it had water in the oil. We used john deere hydraulic oil. It has somewhere between 2000 to 3000 hours. Everything works good execpt when you go up and down large hills the the low oil light comes on and won't let you move the loader or the bucket execpt to go down, when you drop the bucket sometimes the light will go off and contiune to work other times you have to shut it of for a few minutes. Sometimes when you restart the pump seems to howl. The oil is right to the top of the full mark siting and not running. We checked the inlet screen many time and nothing. The filter were changed everytime we flushed. It works very well when you stay on level ground, but if you go up and down a hill it will act up. It will do it if you backup the hill or drive foward. Any ideas would be appreciated, Thanks in advace Brent!