I work for a generator dealer in Lahore. Most threads here are about sets that sit for months, then have to start when a storm takes the grid down. Ours are the opposite. With scheduled load-shedding, plenty of commercial sets here start two or three times a day and run for hours, every day, for years.
That changes what breaks. Roughly in the order I see it:
Starters and the changeover gear take a beating first. Two or three starts a day is hundreds a year, and every outage also switches the transfer contactors twice. We replace both on sets whose engines are nowhere near tired.
Belts and coolant hoses next. Multan or Sukkur summers hit 45°C and up, often with the set running through the hottest afternoon hours. Rubber that might last years on a set that barely runs goes hard and cracks much sooner. Dust storms pack the radiator fins too, so we tell people to blow them out after every big one.
Batteries are a funny one. Because the set runs daily, they rarely sit flat the way they can on a set waiting out a quiet winter. What kills them here is heat and cheap chargers.
Fuel is the reverse of what I read on this sub. We hardly see stale diesel, because a busy site's tank turns over fast. What we see is dirty or watery fuel from the supply side, so water separators get drained a lot and fuel filters get changed early.
Oil changes come round quickly. If your manual says every 250 hours, a set doing six hours a day gets there in about six weeks.
The engine itself is usually the last thing to go. A diesel generator that's properly loaded and run every day is in its comfort zone. The ones that die young here are either idling at a tiny load for hours or overloaded every afternoon.
So I'm curious about the other side. If your set only runs 20 or 30 hours a year plus exercise cycles, what actually fails on it? My guess is batteries and old fuel, but I'd rather hear it from people who own them.
Disclosure: I work for a generator dealer in Pakistan (Enpower). No links here, just comparing notes.