You should check out this thread :
http://www.bikeforums.net/showthread.php?t=299673
Another cause for sticky return is the pivot adjustment if you have two nuts on the very outer portion of the caliper. The acorn nut (outermost) is a locknut that holds the adjustment in place. The inner is the adjusting nut. Use two 10mm wrenches, back off the acorn nut and then back off the adjusting nut just a little. You have to hold the adjusting nut in place while you tighten the acorn nut. This will free up the movement but make sure you don't do so much as to have the brake arms wiggle back and forth (grab the brake lever and rotate the wheel forward and back, your brake arms will "flex" but they shouldn't wobble).