There are little rubber O-rings which hold the adjuster barrels onto the cantilever arms when the straddle cable has been released. Mine have rotted and fallen off, which doesn't affect braking but does mean the barrels fall off when I switch wheels or what have you.

I can't find quite the right size at the hardware stores. I can't find a way to contact SRAM/Avid directly, and the local dealers are scratching their heads. Anyone had the problem and figured out how to solve it?