That’s a lot of hours. Years ago we had a machine powered by those engines. They were mounted on a trailer and powered a hydraulic pump. The trailer was pulled around off-road and the engine was running wide open 10 hours a day in very dusty conditions. I would say on average though it was only used 10-15 days a month but they were hard dusty days. In my 9 years of working with this setup I think we went through three or four engines. The oil was changed regularly and checked daily I think the dust and running while bouncing around on a trailer and WOT conditions got them.
In you scenario with over 8000 hours I would say you are on borrowed time. It may last a lot longer it may not. Regardless it sounds like it is an important engine for you so I would recommend buying a spare and having it on hand for when the day comes that she let’s go so you can swap it out and keep going. Swapping the engines is quick it is the finding them on short notice that is tough. I can tell you a couple stories of engines failing on us on holiday weekends and driving across several states to pick up a replacement so a crew of six guys wasn’t sitting around unable to work.