If my seat post clamp was loose, it would simply slide down under weight. So you're saying it does rotate right to left? You can't have it not moving top/bottom/right/left all at the same time.

PS Boy what a useless post on review. You are saying it moves right to left, but not because the seat post clamp is loose, just some inherent play elsewhere...doh. I'd say it's inherent unless there's a built in adjustment for it, but not having any idea of what suspension post you have...