Over years of working in a mechanic shop and shopping Craigslist, I’ve noticed here and there that people will claim that their old car is still equipped with its original factory-installed fuel pump or fan belt or water pump or whatever, despite the vehicle’s high mileage. “Pulled the brakes apart today. The car is still using the original brake rotors.”
Usually this is 3 or 4 owners in.
Unless they have access to every service record from day one, and know that they aren’t missing any, how do they know that it’s an original part? Do they just see dealer-installed OEM parts and assume they’re the original ones? Kinda confused here. Maybe I’m missing something obvious.
Sometimes there are really obvious revisions to parts. For example early E90 N52s got metal thermostat housings. The replacements are all plastic now. So if you pull off the thermostat housing and it’s plastic it’s been replaced at some point. There are more subtle things like that. The N52 again factory aluminum bolts have blue paint but none of the aftermarket replacements are marked blue.
Most people don’t keep track of this stuff and don’t really know as others have said.