Is it Common For Chain Tensioners to Unscrew Themselves?

[EricSilver]

Car: 2008 E350 with later M272 Engine.

For the past three weeks I noticed an increasingly severe oil leak in the front-right corner of the engine. Upon closer inspection, and after a costly "repair" by a shop that misdiagnosed it as the oil pressure sensor, I saw that he leak was coming from behind the alternator. The only thing there is the timing chain tensioner.

After reading how-to's and watching instructional videos, I decided to do the repair myself. What shocked me was that the tensioner was so loose that I could unscrew it by hand!

Is this a common fault??