There is a suction screen behind a three bolt flange at the base of the shuttle clutch housing, did you remove and inspect it? What kind of oil have you been using in the shuttle clutch? PS: Your dozer is a Yuchai. Jinma doesn’t market bulldozers.
It appears that there was ATF fluid in this unit. This is how it was when I got the unit. I did not know there was a screen there. I will check it today. Do you know the easiest way to remove shuttle clutch? It seems that would be less work to pull engine than remove entire rear of machine.