I have a 1996 JD 955 with a little over 100 hours. I was mowing a few days ago and tried to raise my mid mount deck and it would not raise. I use the rockshaft controls to raise it and the 3 point hitch still raises fine, but not the deck. Nothing appears to be wrong, lift arms still in place, checked hydraulic fluid, everything looks fine. Any ideas what may be the problem?