I've had the same sort of luck - every part is different - with Dorman parts, so even many of the big brands have succumbed to the cheap outsource, zero QC approach.

FCP Euro offers lifetime warranty/satisfaction guarantee, which sometimes helps me decide to risk an aftermarket part.

Otherwise, the cheap online dealers (Husker, Morristown) can often best the local parts stores and -always- beat my over-retail local dealer.

If it's a reputable brand (Bosch, ngk, etc) rock auto is often the cheapest.

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David.X5
2001 X5 4.4i Sport
SOLD! at 160k miles