[old_tv_nut]

D'oh. Now that I look again, this is to be expected because the delay line is not driven from a low impedance (cathode), but high impedance (plate). To do the check you wanted to try, both ends of the delay line should be disconnected and then the jumper put in its place. You are seeing multiple reflections in the delay line when it is still attached.

If the shadow image without the jumper is at the same spacing as the one you see with the jumper, that is the same triple transit effect. This circuit does not necessarily terminate the input of the delay line correctly. Therefore, if the output termination is not perfect (or the delay line impedance is not nominal at all frequencies), some energy may be reflected back to the input and will not be damped there and will reflect again and return back to the output ("triple transit").

This tells you that if none of the components are out-and-out defective, the set may be operating within factory tolerances, and they all were subject to a bit of triple transient effects.

At this point, the delay line is no longer very suspect. Instead some trial and error variation in the output load components may improve things. L13, L14, R63, R64, and maybe L15 can all have an effect. But don't be too surprised if you find that you can't make it much better, and mainly worse. The fact that R64 is the only 5% resistor in the area is a hint. You could try tuning the L's (to larger inductance only) by bringing a core or some iron on a stick next to them. If you had a stock of peaking coils, you could try various values.