When I changed my tensioner in 2007 on my 1991 300CE, the old part was dated 1996. The new ebay crap part I put in lasted a whopping 4 months. I then went with a more reputable internet seller, and so far so good. If you want a ten year part, you'll probably have to go with OEM. If you want a cheaper part, there are plenty out there. Just be sure to get what you pay for.

1991 300CE
2000 C280