There is a city power plant (population ~2,000) located about 25 miles from me that had diesel engines that powered electrical generators. The city used these engines as their main source of electricity until sometime after the year 2000. They actually ran continuously for several decades without shutting them down and would change oil on these engines while they ran. They shut them down in the late 90s to overhaul them. I remember reading in the city paper that nothing was really out of spec. They just dropped in the piston rings and main bearings and continued to use them for a few more years.
They were eventually shut down by the EPA. They continue to sit in the same spot that they have for over 60 years, except they are not running at the present. Every now and then the city talks about getting them up and using them again, but the cost to certify them by the EPA is mindboggling.