Hey Fred,
It does sound like something going on with the record section of the machine.
First, I'd check with the former owner to see if he has any knowledge about this. He may have tried to bias the machine himself or maybe worked on it and plugged the wrong multipin in the wrong socket. Anyway, it'll give you a chance to let him know you're having problems with it.
Do you have a service manual for it yet? If not, you might be able to figure out if it's a problem with the circuits or an adjustment problem by trying to do the adjustments yourself.
Make sure that the entire tape path is spotless. I can't tell you how often left channel imbalance can be fixed by proper cleaning of the guides and heads on this machine. The left channel is
always the outermost part of the tape and because of the angles involved you have to be methodical to clean up underneath the head shield.
Past that, you should check out this detailed alignment and biasing procedure;
http://www.analogrules.com/basicalign.html#biasLet us know how it goes.