One schedule that I am aware of is a top end overhaul at 8000hr., a complete overhaul at 16,000 hr., a top end at 24,000, etc. The newer sets use a computer algorithm to determine overhaul frequency and extend the time for lightly loaded sets.
The basic check points will be the insulation resistance of the generator and, if possible, the exhaust temperature of each cilynder under load.
The overriding consideration is the fuel economy. These sets will each burn about two million gallons of fuel a year. The purchase price of older less efficient sets should and usually does reflect the increased operating cost. I have seen a purchaser go with a slightly less efficient set when it was a make that their crews were familiar with and were trained in overhaul procedures.
I hope thios is helpful even though it doesn't exactly answer your question.
respectfully