Mine's a Kryptonite but i had the same issue - i rolled a rubber o-ring over each end of the U-shackle to bridge the gap between the plastic coatings of the two parts.

Kryptonite had already fitted similar rubbers, but they weren't quite snug enough. If they're too snug you'll make the lock mechanism sticky - i have to push on it only slightly to prevent turning the mechanism under load.