I looked at the schematic, I don't agree with their voltage, I did calculation and wrote on the copy, double check my work.
1) It said Q109 and Q110 are +18V and -18V regulator resp. Why say 17.7 and -18.4, should use +/-18V.
2) The two opamps used in Q106 got swapped, they don't match Q105 if you look at the schematic. pin 2 and 3 should read 0V.
3) I calculated the current through R117 to get the tail current of the differential pair Q101. Assume the Vgs is -1V for jFET, so it's 19V across R117. current I=V/R= 19V/5.6K to give 3.4mA.
4) from 3.4mA, assume the two jFET share equal current, so it's 1.7mA through R119 and 1.7mA through R121. So voltage drop across the two resistors are 1.7mAX5.6K=9.52V, so the voltage at the sources of the two jFET is 18-9.5=8.5V..
So pin 5 and 6 of Q105 is 8.5V, not 5.97V. Even 6.4V is way off.
5) Output of pin 1 of Q105 is not predictable because it is used to adjust the imbalace at pin 6 of Q105 to get 0V at pin 7. You cannot call the exact voltage at pin 1, it can vary up to +/-1V around 8.5V depends on the matching of the Q101. I don't agree the reading of -1.3V.
You can see from the calculation, it does not even agree with the reading measured by OP. Take a look at my calculation. You sure the schematic is the same as the real circuit given so many things wrong on the schematic already? Double check my calculation AND trace through the pcb to make sure the real circuit match the schematic.
BTW, pin 2 and 3 in Q106 still wrong according to the reading by OP in the first post.