Its easy to dissect a part superficially. E.g. spark plugs with same numbers and supplied by same manufacturer
The difference are subtle in them, like they will have a heavier electrode and will be provided with encapsulated antisieze on the threads. And have top select shells.
Same with brake, rubber or suspension parts. The difference in brake and rubber are their body compounds, the manufacturer will not give same product as OE in retail market. (Business agreements)
Have you experienced supply business as OE vendor? If not next time when the auto manufacturer expo is held in Pk go visit them.
The only unique difference in manufacturers are american ones, you can buy AC delco parts in retail with genuine GM part numbers - they are same as factory items. Same with motorcraft for ford and mopar for chryslers.
The spare parts brands are their own shootoff of the parent co.
This is why I love their systems. Meanwhile all japanese manufacturers wont even entertain you for specific items
E.g. mazda fl22 coolant is similar chemistry as toyota pink, long life formula coolant. Only sold as premixed to which customers complained a lot.
Fords which were based on mazdas also used same stuff and then later on provided the same coolant in concentrate form under a motorcraft part number.
