If the level problem switches channels when you switch the mic inputs plugged into the ua5, then your problem is in one of three places, the caps, the bodies or the mic cables. I'd swap each of these around, one at a time (i.e. start by switching the caps from one body to the other but leaving the rest of the setup unchanged). If swapping JUST the caps doesn't cause the level problem to switch channels, your caps aren't the culprit and move onto the bodies by swapping JUST the left body for the right body while keeping the caps and cables hooked up as originally, etc.
Once you identify the problem component, go to the manufacturer/retailer and get 'em to replace.