O.K. this is the story. I had my tensioner replaced two years ago with Porsche Dealership, ( approx 3500km ) so when they replace the tensioner the bolt is removed and re-used and torqued back together when the new tensioner is installed.

Anyway, every time the steel bolt is removed from the aluminum block it takes some threads ( aluminum ) so when the original bolt is re-used and re torqued sometimes it may not be as strong as per original torque. Its not suggested to use locktite on the bolt threads as its steel into aluminum.

So I was told if it comes loose again the procedure will be to remove the rear bumper and heat shields, remove tensioner and drill a new hole into the aluminum block, insert a steel sleeve an put it all back together. 4 hrs labor plus parts. Original tensioner gave way at 32,000 kms

 

I am assuming the bolt holds the bearing sleeve which the tensioner rotates on. During periods of non use can the tensioner seize on the sleeve and then during return to use this breaks the torque lock and allows the bolt to unscrew. I wonder if this problem occurs generally early in the driving season of winter stored cars. Tensioner tension release during belt replacement may be another culprit. I put a mark of red nail polish on my bolt so I can Identify bolt movement easily. It is hard to get the proper torque on this bolt without removing the heat shields. If one were to drill a hole in the heat shield similar to the one for the spacer bolt that is required to be removed during serpentine belt replacement it would be easier but due to location the bumper may still have to come off.

 

This is exactly what happened to mine. The bushing was seized so when I did my belt it loosened back up. I am worried people will replace just the tensioner shock, when they also need to replace the lever with the bushing. The new lever is a revised part number starting with 9A2.