Unfortunately the tentioner in these 116/117 motors is not a ratcheting one. I replace a tentioner when it regularly looses its pressure overnight. This is noticed by a rattling sound on start-up that goes away after oil pressure fixes the tentioner. This rattling is what does in the upper rails when they are brittle. It will happen occasionally no matter how good the tentioner. If I heard it twice in a hundred starts I would probably replace the tentioner. Maybe twice in 50. if the rattle didn't cease instantly with oil pressure on the gauge I would also replace it.

The point of doing nothing is that since you will need a valve job when it comes apart anyway the only difference that letting it fail will bring is the need for four exhaust valves, maybe a couple intake but not often. All the labor will be the same and 80% of the parts which is the small part of the job.

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