I see no technical reason to change it now. The part is very durable. I believe the only problem that ever occurs with the tentioner is contamination from debris in the oil. The act of loosing pressure over time is a matter of the check valve not holding and I have always thought this was due to oil grit in the check ball. As a result of this concept mileage is not really an issue. The issue is performance.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician