I run conventionally but I have several MTH locos with many hours on them. I have a RK Y6B that has, easily, 3000+ hours. It's had the traction tires replaced, and the tether is showing signs of where and I put some electrical tape on it, but otherwise fine. I have a GTEL that has nearly as many hours on it. Both still run fine.
My experience is that some locos (Lionmaster big Boy wore out, etc. ) wear out their gears and rod bearings and all at between 2500 to 4000 hours, but frankly I have few locos in that category so I cannot generalize.