Technology issues aside, why would you want to spend $600 to replace a part that isn't broken? Belt tensioners are easy enough to replace, so run the one you have until it actually *needs* to be replaced.

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"It's not about how fast you can go, but how well you can go fast."

Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles