Fleetwood model 4068... Advice?

[electroking]

You mentioned that the voltage on pin 6 of the 6AQ5 tubes was 265 instead
of 230. Something might be open in the network formed by R21, R24 and
R13, which would explain the wrong voltages measured on the 6AU6 tubes.
Those parts are nearly 50 years old (just like me), don't forget, but
fortunately there are not too many of them. Good luck.