Back story: The stock saddle failed on my Yuba Mundo. The saddle clamp had got loose without me noticing, the saddle worked its way all the way back, and eventually the rails bent until they popped out of the saddle body.

I replaced the saddle with an old Selle Royal salvaged from my disused hybrid bike. I am having problems now with the saddle slipping backwards in the clamp. I can start it all the way forward, and by the end of a 5 mile commute it will have slipped all the way back until stopped by the bend in the rails. I don't know if this is the same problem that broke the original saddle, or if I'm having this problem because riding the first saddle loose damaged the saddle clamp.

I am tightening the bolt as much as I can (I have the 4/5/6mm Park Tool hex wrench). Is it just a question of needing more torque? I have a ratcheting wrench with a 6mm hex bit I could try; that would give me a longer handle.

But I'm wondering if the saddle clamp is deformed and no longer is able to pinch the saddle rails perfectly. Does that seem plausible?

My questions are:

1. I don't see any indication on the saddle clamp regarding how it goes together. It looks more or less symmetrical, but is it supposed to face a certain way? Likewise, the rectangular nut that secures the bolt could align either parallel or perpendicular to the long side of the clamp. Does it matter which way?

2. Can a replacement saddle clamp be purchased separately from the seatpost body? (It's the two piece / one bolt kind with a grooved bottom that sits in the concave grooved surface of the seatpost and allows angle adjustment that way.) The seatpost is an unusual 31.8mm diameter, 500mm long seatpost that Yuba sells for $40. Would be nice not to have to replace the whole thing.

3. Am I wrong in assuming I could just swap the saddles over? Could the Selle Royal saddle rails be slightly narrower than the clamp is designed for, and thus won't stay put?

Thanks.