If you play CD's or a tuner, are you getting this same off balance? If so you might just have a small difference in your hearing ability which can easily be allowed for by turning the balance control if it occurs only on some records, or if it is on all you can move you right speaker a bit closer to you (an inch or two might be all it takes to bring them back into balance.) If it is only LP's you might try increasing your VTF to the max recommended by the manufacturer and check your anti skate (although this shouldn't make a difference, its possible that it could).
Another possibility - if your listening position has you facing dead ahead between the two speakers and side wall and ceiling/floor reflections are the same, try twisting your chair so that you are looking into the center of the space between the right speaker and the center of the stage. If you find that the image moves back into the center go see an audiologist for a hearing test.
Another possibility - if your listening position has you facing dead ahead between the two speakers and side wall and ceiling/floor reflections are the same, try twisting your chair so that you are looking into the center of the space between the right speaker and the center of the stage. If you find that the image moves back into the center go see an audiologist for a hearing test.