I looked at a lot of combines before I bought the one I now have (87 M3 2400 hrs, mint) At 3000 hours, you can expect a rebuld of heavy wear areas--cylinder bars, concaves, drive belts, elevator chains, esp. if the combine has done a lot of dusty crops like beans where a lot of soil particles enter the machine. At 4000 hrs, most chains would need replacing along with auger flighting,and bearings that are subject to heavy high power or oscillating loads. This done, the machine should last that long againn, but more wear areas show up--raddle floors, auger bottoms--and engine_drive trains after 5000 or 6000 hours could reasonably be expected to need a rebuild_overhaul. That said, I,ve seen 2000 hour machines that should have been parted out---never shedded, never cleaned out after harvest, cab trashed, dented. Then I remember looking at an 84 F3--5500 engine hours--the carpet on the cab floor was wore, but the rest of the machine was excellent. It boils down to what you said--owner neglect_operator abuse will soon wear any machine out. If the machine has been serviced per the owner's manual, the hours don't have as big an effect on price as does the condition of the machine. There are 7500 hour machines performing as dependably as ones with far fewer hours. Since almost every part can be replaced_rebuilt, the life time of a machine depends more on wether it becomes technologically obsolete or wether it can be replaced for less the the cost of a rebuild. This doesn't answer yuor questiopn, but then the answer will be different for every owner. Ben.