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Submitted into the show, the game lost red control (red gun wide open) during pre-show testing and was withdrawn :(
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On the bench the chassis showed the same problem as in the cabinet thus confirming a problem with the chassis rather than the CRT. Comparing red with green and blue on the neck board showed that TR33 (BF871) was only 33V versus ~330V-360V on green & blue. Pulling TR33 and testing it suggested it was OK and replacing it on the neck board with another had no effect on the problem. Attention turned to TR32 (BC537) that drives TR33. Pulling that and testing it showed it to be bad and replacing it (with a BC237) fixed the red drive.
However the red output was now very low. Poking around with a scope and comparing the red input to the neck board with green and blue inputs showed that the red signal was very low by comparison. Checking the video input from my test PCB confirmed that red, green and blue levels were equivalent going into the chassis. Tracing back from the neck board through the pre-amplifier chain on the chassis with the scope found that the signal was good into the base of TR20 (BC547) but no different at the output versus amplified on blue & green. Replacing TR20 (with a BC237) fixed the red signal level and the picture looked good.
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Back in the cabinet the chassis seemed to be working fine for the most part but red still looked a bit weak compared with the MAME as a reference (that also matches the display on my test bench).
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Back on the bench, cross comparing the chassis outputs to the neck board proved that red was off compared to green & blue. This narrowed the issue to the pre-amplifier section on the main chassis. Working back from there, the signal at R93 looked bad, stuck mostly at 5V versus blue and green that were healthy looking 0V to 5V signals. R82 looked unstable/low. R34, the base of TR11, also looked bad. However the game RGB input was definitely good as were the inputs to the brightness pot RV1/2/3. I decided to go with pulling and checking TR11 (BC547B) - the transistor checker found it to be bad. Replacing TR11 (BC547B) with an equivalent BC237 brought red back to looking the same as green & blue all the way through the pre-amplifier and the picture looked to have a healthy red.
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Back again in the cabinet the game looked much better with all the graphics components present and the red looking good. A few hours of burn in testing did not reveal any further issues.