Hi slbender,
The place to start is always to verify the power supplies, paragraph 5-53. Post the results of your measurements.
Is the +158 Vdc correct? You say the zero marker is squished off to the right, this sounds like a horizontal deflection problem, in addition to the dim display.
What are the results of the Display Adjustments, paragraph 5-58? Is there any noticeable change in the display?
It may be necessary to verify that the CRT gun is properly biased, that the grid is not holding the electron gun near cutoff. Both elements sit around -2.9 kVdc so extreme caution is required to measure the differential between the two. Varying the intensity control should produce something like -50 to -15 Vdc between the grid and cathode, corresponding to minimum and maximum intensity.
If you have a suitable HV probe, carefully measure the CRT cathode (pin 2). If the -HV is low, then proceed to check the HV oscillator and that the control amplifiers Q23 and Q22 are not throttling back Q21 base bias.
Rule out the easy to test items first before jumping to the conclusion that CR5 may be defective. It is entirely possible the CRT emission has fallen off with many hours of operation. If all supply voltages are correct, the -HV correct and grid to cathode bias is reasonable, then low emission is pretty much confirmed.
I do have a 3580A and can make some measurements, if needed. I use my 3580A as an auxiliary digital storage display, connected to an HP141T.
RF+ Tech