I just bought a hybrid from eBay, it arrived this morning. The bike is fine and I've got everything tuned up but there is a problem with the suspension seatpost. The seat can twist a bit even though it's securely fastened in the seatpost. It's just the top part, the bottom goes in fine into the seatpost. I've tried locking the suspension using the nut at the bottom but the seat still twists. Any ideas? I want to avoid buying another seatpost, I've spent enough money on bikes, tools, parts and acessories already :S

Thanks.