I'm going to be doing my tensioner for the second time in 5 months. I tried to go the cheapy route and buy the tensioner off ebay. The first one I got was DOA but I didn't realize it until a year later when I went to put in the part. A quick check for a good tensioner is that the pulley is in line with the 2 flats of the aluminum bushing. I complained to the seller and he sent me another one at cost, ~$50. Both appeared to be the same correct part number but with the manufacturer insignia ground off. I installed it 5 months ago and it just failed. Hope I have better luck with a unit I got from Autohauz for $100.

glenmore
1991 300CE
1990 LS400
2000 C280