Hi,
I have a cross check also and about 3 weeks ago the bolt holding the seat clamp broke in half as I was getting some speed up. I don't know how I was quick enough to stand up. Anyway I had my saddle as far back as it would go, a bit past the nmbers on the rails. I am assuming that helped or lead to the break. I replaced it with a mountain bike seat post thinking it would be stronger - it has a two screw clamp.