Parts aren't so expensive if you shop around - ECS Tuning and FCP Euro have some decent aftermarket parts. Husker BMW is usually the cheapest for dealer parts. BMW PNPC is a program that lets you compare prices on dealer parts across ~20 sources. Fairfax BMW seems to be starting to sell online at pretty good prices now.

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