i have a 2020d yanmar that i'm having a problem a problem with the lift. the lift will come up , but it doesn't want to go down. it will bleed down in 10 minutes or so. when i use the tractor and it warms up good it works ok. them when it gets cold same problem. i've change fluid and filter and cleaned the screen. also there is no rate of fall knob on this model and valve is open any help?? thanks , todd