I just checked mine again in some better lighting. It has a slight oil coating on the side on the shock part above and below the rubber bellow. I feel it is important to mention, that I haven't had any issues so far, but I'd like to catch this before it becomes one.
I would appreciate if anyone else could do a quick visual inspection of their part, to see if this is normal?
Mine is a 2018 with ~8K miles.
To be on the safe side, I placed an order on a new tensioner, part no. 12669076.
With parts availability here in Europe, I don't want to be left stranded somewhere if it suddenly stops working.