I really wanted the hose clamp to work, but I have a classic NYC antitheft chain on my saddle. Can't take the saddle off and I couldn't get the hose clamp back together after I opened it up.

So I had no choice but to go the the LBS. This will forever be the mystery problem with a mystery solution. The very busy LBS fixed it while I waited (on a sunny Sunday afternoon). The mechanic speaks little English, and I speak little Spanish so we couldn't really communicate. They didn't charge me, so I didn't press the point, and hightailed it for Central Park.

Bike is fine now, and thanks for the suggestions. At least I know what they might have done.