These units used to be a favorite of mine.
Theydo suffer from dry solder joints and PCB cracks.
Look for and touch up any dry or suspect solder joints.
I'm having difficulty understanding I'd this is a playback or record fault. Try using a playback level alignment tape and check both channels are aligned correctly. If its a difference in the record levels then check record level alignment. You may also have some problems with tape bias.
Z
