@demonkuro Sorry to be blunt, but people here who help you have their way of troubleshooting issues. To get the most out of their expertise, please do the measurement they asked so they can better help you. Extra measurement may help, as long as they are well documented. For instance, are the voltages marked on you schematic from the R channel? Also, doing shotgun-style component replacement without narrowing down to a suspect is rarely effective. Apparently the problem on the right channel is a balance issue. The final stage offset servo is most likely working fine. That's why replacing Q30 thru Q33 didn't help.
Measuring Hfe of the transistors in circuit would not give you accurate results, especially when the base and collector are shorted together in the circuit.
Assuming the voltages marked on you schematic are from the R channel. They look reasonable. There is one volt difference between the cathode of the EL34s (457V-456V). The triode-connected EL34 has a mu of about 10. For a matched pair under the same current, 1V of difference should create about 10V of difference between their anodes. But now there are 50V. That could be caused by different currents from the CCS. Measure the voltage drop on R18 thru R20, R17 and R14, and you'll get an idea how much current is flowing through the CCS. Do the same on the other arm and compare.
To check the operation of the balance servo opamp that seems stuck, I suggested that you 'Follow the trace from O+/O- all the way to IN+/IN- of the opamp and see where the problem is.' I didn't see any feedback from you. Now that O+/O- differ by 50V, points C and D should be 5V apart, IN+/IN- of the opamp should be clamped by the diodes to approx 0.6V in the correct polarity, and both opamps should output close to rail after a few seconds. If you don't get the correct IN+/IN- voltage, you may have a short or a diode installed in a wrong orientation. If you do get the correct IN+/IN- voltage but the opamp still outputs zero, you may have a bad chip or a leaky cap (0.47u). BTW, film caps (polypropylene) are recommended over ceramics in those locations for lower leakage.
It's a pain in the butt to remove the C3381s, but quite easy to check if they work correctly in circuit. They are used as current mirrors. Current that flows thru R86 should be roughly the same as the current that flows thru R84. Measure the voltage drops and you'll have an idea.
Remember that I asked you to measure the top and bottom voltages of both active batteries of both channels? That would tell us if the imbalance is from the front-end or back-end. In other word whether the imbalance is before or after the active batteries.
Before the balance issue is resolved, it's probably not necessary to repeat the hour-long tests. A better way is to take as many points of measurement as you need in one shot, shut off the power, analyze the data and go from there.