Not on my X, but I've used/installed about 4 aftermarket axle assemblies in the last 3 years (because of torn boots.). No problems to date. Many independent shops that have knowledgable mechanics will use aftermarket. If available, I try to get the NEW versus REBUILT aftermarket.

But I have to admit, I usually sell my cars before 100-120k, so even if I replace the axle at 70k, I don't expect to be in the car for a whole lot of miles more. But no problems I've seen.

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'05 4.4i Toledo Blue