Proac Response 3.8 stereo imaging is not centered

I picked up a pristine pair of Proac Response 3.8 speakers recently. They sound lovely, however the sound on one side seemed slightly weaker than the other side with the stereo image or soundstage offset to the louder side. This has never been an issue with my other speakers. Speaker cables are the same length. Switching the speaker wires at the amp output doesn't change the asymmetry. Switching the speakers from left to right and vice versa does change the asymmetry. So my conclusion is that the one speaker is slightly louder than the other? The individual speaker drivers are performing fine and the musical presentation is otherwise fine. Could the crossover components be the problem? Any other ideas to troubleshoot this?