Has anybody compared the notch method to the gauge method just curious to the findings.

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84 300 Turbo / 320,000
96 E300 D / 55,000

The tensioning rail can be checked if you remove the tensioner and get the chain out of the way. The amount of abrasive material remaining before the chain hits the supporting plate is the critical bit of infomation that you're seeking.

However, sometimes these components don't simply wear out.......they fail. There is usually no possibility of determining when such a failure will occur.

The work involved to get to the oil pump would dictate that you do the repair while you have it opened up.