Hyd oil from the engine timing hole indicates the hyd pump drive shaft seal and/or main drive shaft seal is leaking oil into the flywheel/clutch area.
The shaft seals reside in the tachometer & hyd pump drive housing. You will have to split the the tractor the same as doing a clutch job as in pic #1.
Pic 2 is what you see as split. The leaking seals are in the assembly marked "Tachometer drive housing". Slide the bearing and spring off the shaft. Remove the clutch yoke. Unscrew the tachometer drive at the top of torque tube. Remove the 4 cap screws on the drive housing assembly and slide it out.
Pic 3 is a breakdown of the tachometer/drive housing assembly. Shaft seal G10422 is the hyd pump drive shaft seal. The main drive shaft seal is G10421 for tractors before serial nr 6097696 and G13816 after. 310 will be the former p/n unless the hyd pump has been replaced with the later style.
Shaft seals are avail from Case or crossed to Chicage Rawhide p/n and avail at Napa.