I have an industrial John Deere 401C. My loader stops working intermittently. Sometimes, if I shut the tractor off and start it back up again it works. Sometimes it will raise slowly, sometimes not at all, sometimes it works perfectly. The power steering stopped working briefly, but then started again. I have been able to get it to work in the past by adding more hydraulic fluid although this takes the level well above where it is supposed to be. The rear hydraulics work fine. Any suggestions would be appreciated. Thanks.