[BillDWVA]

I’ll do my best to make some suggestions:
1) Poor sound quality. First thing is to check that this is caused during recording by playing a tape pre-recorded on a known good machine. However as much of the circuit is common to ‘record’ mode as well as ‘playback’ the first test would be to trace the audio signal through the various stages to find where the degradation occurs. Another test would be to inject an audio signal from another source and monitor it to check its quality. Distortion or low ampilification may be caused by bias voltage on one or more of the amplifier valves being out of range caused by an out of spec resistor. I only have a diagram for a Series 2 in front of me but the components to check would be the resistors from cathodes to chassis and control grids from the anode circuit of the previous stage. You mentioned that the sets have been ‘recapped’; There is a possibility that the bias trap is out of tune now and the audio output stage is being saturated by bias current when it is in ‘record’. This can be checked by hooking up your ‘scope to amplifier side of the trap (a capacitor and variable inductance in parallel - L3 and C22 on this circuit). You will see the oscillator waveform when the set is switched to ‘record’ and the inductor has to be adjusted for a minimum bleed-through. I don’t think that the equalisation circuit would cause such noise unless something was badly out of spec. Was the machine OK before it was ‘recapped’? Always best to replace one component at a time, testing as one goes.
2) Sticking meter on these can only be some mechanical locking. If it is a Sifam meter then it is high-quality instrument, from my experience. Check again for a bent needle or end stops - these get squashed in by a detached glass.
3) Incomplete erase; Low oscillator output? Poor plug/socket connection or dirty contacts? misaligned or very dirty head?
4) Weak winding; Have you checked that the brake is fully releasing? Turns-counter drive gear binding?
Hope this helps?
Bill