Horizontal lines in a Panasonic

[MIPS]

I'm cleaning up a Panasonic AG-RT600A Time Lapse deck for a project that requires a very long recording time. I've already gone through the recording mechanism to clean the heads, rollers and capstan, plus demagnetized the capstans (NOT THE HEAD DRUM). I ran through my stack of 3M broadcast quality S-VHS tapes to find one that wasn't jittering badly due to age (plus run them under a bulk eraser plus a retension) and now I'm at a point where the playback is perfect with the exception of one thing.
On all the tapes I tested there's thin horizontal lines that randomly fade in and out as they move downwards on the screen. They aren't too evident when the picture is moving but on static images like a test pattern it is quite obvious.



They feel like time base errors. I don't have the money for a TBC.
I'm not sure what else I should be checking here other than tracking. I'm using high quality tapes in a freshly cleaned deck which reports 23291 hours. (okay, that's a bit high but it was used as part of a security system)