Nakamichi 680 three head 2speed cassette deck

Nakamichi 680 I purchased new in 1981. I used it a lot for many years but have not recorded with it for years and used it for listening only occasionally. Going to use it now, I have found some issues.
All transport functions work correctly except for the switch to select half speed which feels odd when when I try to change speed and will not change to 15/16.
Plays fine at normal speed
Both metering modes work fine.
It will record, but not correctly. Levels for Dolby calibration and recording fluctuate and/or can't be set to proper values. Recordings won't balance left to right and I hear distortion even at levels well below normal. The Dolby calibration tone is not the same level for both channels. Whether this is the tone itself or the meter in calibration mode I don't know.
Since I can't get into half speed, I can't say if the same conditions exist there.
Cosmetically, excellent condition. The opening in the top panel gives access to the bias level pots. When I did a lot of recording I used to set the bias for each individual cassette so I made the opening so as not to remove the cover all the time.
I will answer any other questions if I can.
Since I so seldom use the deck anymore ,I am not inclined to invest in cleaning/adjustment/repair so I have decided to sell even though I know I am probably going to regret it. It made flawless recordings and had the best metering display ever.