Hello,i Have the above tractor with this strange problem and cant get to the bottom of it,the lift arms will lift perfectly but will not drop even if standing on it,after a few days the arms will gradually lower back down to bottom but as soon as i lift to the top the same thing happens,this happened out of the blue one day,i have stripped down the distributor and cleaned everything but to no success,i have been working on zetors over 30 years and this is the first time i have seen this issue,has anyone ever heard of this or have an idea of whats causing it?Thanks