It's funny I stumbled upon this thread. Just a few days ago I realized I'm having the same problem: center image is slightly to the left- confirmed with mono recording and few listeners, other than myself. Everybody was absolutely certain.
I'm sure the problem is new, and I haven't changed anything in the system.
I have an inclination to blame my power amp. (BAT 75 SE), maybe one of the tubes is giving up.
What is the easiest way to check the output signal in both channels?, and what should I use for that purpose?
Please, help.
P.S. I haven't done any speakers swaps yet ( they are quite heavy).