owners manual/ advice on K 1501

[big bubba]

friend of mine recently bought a garden tractor model Kubota 1501. that's all info i got. hydraulics went out (lifting). external spin on hydraulic filter changed by dealer, but had set for several (maybe more) yrs, dealer did not change hyd oil itself. is there a strainer that could be restricted w/moisture/scale? would an owners manual help? regular udt if decided to change?....thx in advance. bb