Same problem - my seat clamp is metal though. Drives me nuts. At least I finally got it where the range of motion is very small and I can deal with BOTH positions. I would like to be able to adjust my seat and have it stay, but have been too lazy to drag my bike into the city a hundred miles away to have the bike shop look at it. I actually just thought they would think I'm nuts or just too wimpy to tight the bolt or something. Okay, I have no idea why I feel weird taking it the bike in for that. Though they will think I'm nuts for trying the Brooks saddle. They advised against it.