JVC PC-30 auto stop problem

[HWTest]

I just bought a pretty nice JVC PC-30, it's missing one volume knob and it has a little quirk.

Regarding the missing knob - how do you solve such a problem? I have removed the remaining knob from the slider because it was hard to operate both volumes simultaneously. I'm thinking about looking for a pair of different fitting knobs.

Regarding the quirk, the symptoms are - in reverse play, auto stop or auto reverse doesn't work, it just tries to spin the left spindle. Auto stop in rew doesn't work too.
When I'm in reverse play and press stop, the reverse switches to forward play (meaning when I press play again it starts playing forward instead of continuing in reverse play).
The left spindle seems to have less torque than the right spindle.
The original owner told me, that all rubber parts are new - belts, pinch rollers, idler tires.
What could be the problem?

 

[HWTest]

I think, I know what the problem is, the rev take up reel assembly.
It consists of the take up reel and two toothed wheels, all of them are able to rotate independently and are coupled by some slipper clutch - sadly there seems to be no adjustment of it.
Between the two toothed wheels seems to be some felt but I have no idea what kind of clutch is between the reel and the wheels.
The lowest wheel has to stop to engage the auto reverse/stop mechanism
I was thinking about interchanging the fwd and rev reel assemblies, to make sure the problem is in the reel assembly but they have different part numbers in the SM, I'm afraid they are not the same (not interchangeable).

 

[HWTest]

I did some torque measurements:
f. play take up 60, back tension 15
r. play take up 15, back tension 5
ff 80
rewind 20