Thanks for the reply, SB. I do believe it is the reel table, according to the previous owner. I'm a bit concerned about doing more harm than good by trying to adjust that myself but maybe I'll give it a shot.
I recently acquired an MTR 90 mk.II with the following problem. The supply reel seems to be ever so slightly off center so that with every rotation, the level of signal drops about half a db on the meters. It's not audible to my ears but makes calibration something of a pain.
I assume this is...