How many hours on engine or is hour meter not functioning? The D-239 was always a hard starter in the cold. The newer versions had higher compression pistons that helped starting in the cold. Re hyd fluid leak from under dash, could be PS pump or PB system. There are actually two master cylinders, one for each brake with an equalizer valve between the two. Unfortunately to fix leaky wheel brake cyl O-rings you have to remove the axle. Splitting tractor will only help a little with brake repairs as master cyls are under battery box. Here is parts from caseih.com:
Good luck with your clutch replacement.