If it were my car, I'd replace the chain, chain guides, and worn gears, and leave the vanos as is. Of course flush the engine as much as possible. I'd also buy the vanos tool kit for about $325 and do the job myself,; there are plenty of good tutorials on the forums. Given the age of the vehicle, even if you got a used 4.6 motor, it would be hard to fingd one that had really low mileage, so similar problems could happen again soon. And I'd bet the total cost of buying and installing a good used motor would be at least $5,000 or more.

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2014 BMW 328i Xdrive
2011 BMW 335i M-Sport
2008 BMW X5 4.8i Sport
2000 BMW 528i 5sp