Tensioners can be weird, I guess. I've had no issues with mine, on my 454. It's still original. It moves a bit, but it's always done that. I did finally replace the pulley itself. I have a new older stock part from ebay to install when I need it. However, on my dad's old 96 truck with a 350, the tensioner seized! I was borrowing the truck, and I was looking at the engine for some reason, and I realized that even though the pulley spun fine the tensioner was frozen solid. I had a new Gates tensioner, in my parts stash, for my own truck, that I installed for him. I'm still kinda baffled by it. Failure usually means pulley/bearing problems, or the arm becoming undampened/loose.