Ive seen a caterpillar genset (IIRC, it was 500kva) with the ability to have its oil changed while running. The setup was rather clever, the oil filter had a isolation valves and a bypass valve. There was also a drain valve for the oil pan. Basically you put the filter valves into isolation/bypass, remove the old one, install new(pre-filled), drain then add 2 quarts 10 times then put the valves in normal position. Never really gets all the old oil out but its enough to keep the engine happy for over 2 years now. Air filters are changed by opening and closing the air box. Visited a cousin in Alaska that serviced a generator that ran 24/7 and that is how they did it.
Each of the fuel supplies had a similar filter setup (it could run on diesel, biodiesel, propane or CNG)
This was the primary power source for the island until the POCO brought in a UW cable. The power from the POCO is very expensive so now its a co-generation plant and is community funded/operated.
The site has 8 of these generators that pretty much ran 24/7 until there is a major failure (blown head gasket, thrown rod, etc) or taken down for overhaul. Every 3 months, the generator with the highest hours is taken down for overhaul. From what I remember, the generators handle the baseload and anything over that comes from the POCO. When the loads are under the capacity, power goes back to the POCO. The generators are governed to always run at 92%.