Gearbox overhaul intervals, field experience knowledge

We operate in the states a G3520c 1500rpm with a gearbox that increases the altenator speed to 1800rpm/4pole SR4B, and would like to know what the in the field experience overhaul recommendations for the gearbox, CAT manual is lil vague and seems overkill.

Right now we only have 10,000hrs on the genset/gearbox and change the gearbox conventional 40wt oil every 4,000hrs with new filter, oil anaylist always look very very good at the gearbox oil change.