Hi Cata2200,
Alot here depends on what environment in which the equipment is working.
When I was working in the Mines, we did our overhauls based on both hours and oil analysis at that time provided by Cat.
We sampled all engines, differentials, gearboxes, final drives, and hydraulic systems at the prescribed hours. We relied on the results of the oil analysis and working hours on the equipment to decide when to overhaul.
Again in this situation, when an overhaul was required we would get the respective Agent to do the overhaul, expensive you might say, but in the long run no. We always got a 5000 hour warranty on the overhauls.
You need to work out what is best for your environment, there is no hard and fast rule.
Regards,
Kevin