OK, Studio guys, here's a challenge for you

[Dave Labrecque]

They were probably recorded on a stereo deck, but it would have been a mono feed.

However... they were duplicated on a mono duplicator, and the pattern of the right track being louder is only on one side... the left track is louder on the other side... this is an artifact of the duplicator.

Understand that I'm suggesting that the print-through audio is stereo-imaged differently than the primary audio; thus the idea of discriminating between the two on that basis (via M-S or some other way).

[CurtZHP]

Voxengo makes a free M/S processing plug-in that may be helpful if you wanted to experiment with that possibility. At least if it doesn't work, you're not out any money.