On JD utility tractors 20 series and up because of the brake pads that run in oil I would recommend changing hyd oil & filter plus cleaning sump screen located in bottom of trans back by hyd filter. I recommend JD Hy-Gard hyd oil as it has additives to help with brake noise. Changing hyd oil will help remove moisture if any has formed from condensation. I'll also add that an internal hyd leak can cause sloooow hyd's. With engine running,3pt raised look inside hyd filler hole for spraying oil which will indicate a leak.