I've got to agree with Eric. Most stories I hear about axle failures are from dry CV joints due to leaking boots. The stock units are very rugged and if you can keep them in the car I think you should. The lifetime warranties are nice but I don't value my time and labor as free so I think the difference paid for a reboot on a solid original axle is worth it.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold