My brother bought a used Ford bucket truck to do some tree work. About a week ago the lift started freezing up occasionally. It seems to be always at the same angle when it stops. After it sets a day or 2 it will work again, but just until it reaches that same angle, then it stops again. It works fine either up or down once it gets past that angle. We looked for a hydralic line that might be binding at that angle but didn't find any. Any ideas?