[David Stringer]

It looks like maybe tape-path out of wack. Since the machine is older, I would guess the exit guide is a little low. When no one was looking, I would use the graphite tip of a pencil to lift the tape a tiny bit higher on the guide and see if that fixed the problem. It sounds like you have a service manual, and the tape path adjustment procedure should be in it. Since you’re not doing new recordings, there is no real shame in using any one of your tapes as the “alignment tape”. You should use a scope and do it right, but if moving the guide a bit fixes the problem, no one needs to know…

David