Mine is the design where it goes through the passenger side of the timing cover. The tensioner has a circlip that acts as a ratchet, only allowing the plunger to index toward the pressure direction. It can't go backward. Basically, if the timing chain goes slack for any reason, you're supposed to remove the tensioner (after moving the air pump out of the way) from timing cover, then take it apart by pulling the plunger all the way through in the pressure direction. Then put it together by inserting the plunger from the other end, but only after the timing chain and guides are in place and the chain is ready for tension.
There are more tips I can give you if you need detail. I wasted three hours on something that should take 30 minutes. I'm still at the steep part of the learning curve for this vehicle.
95 E320 Cabriolet, 131K