After transport & setup the game was operating normally with no issues.
After a few hours of run time the monitor had once again drifted out of focus with the focus pot hard over. The game itself continued to run OK and it made it through to the end of the show albeit out of focus.
At my storage place the game didn't exhibit the same focus drift as it had at the show. I surmised that this was because the game was cold location and hadn't yet been on long enough to drift out of focus (even after a couple of hours). The game would need to come home for more run time.
The CRT had already been tested with the rejuvenator and I'd already measured the focus voltage and seen it gradually climb so I suspected that the LOPT or focus bleeder was bad. The LOPT was hissing constantly so I decided to recover a replacement LOPT & bleeder assembly from a spare chassis to go into this one.
The reclaimed LOPT & bleeder were fitted into the chassis and the chassis tested in the cabinet for a few hours to confirm the focus drift was fixed.
The HT cup on the reclaimed LOPT & bleeder assembly had a broken clasp necessitating a MacGyver repair using a clip from a failed LOPT. After several more hours in the closed cabinet there was still no sign of any focus drift and the game was pronounced fixed ready for show.