Thanks to the helpful Bob Roberts (the Real Bob Roberts, of course), I replaced the guts of the often malfunctioning move joystick on the Robotron. I would guess that the joystick was original to the game, as the leaf switches were pretty much shot. My first game with a 100% working move joystick reached 2,159,100 points. I still need some practice.
Also, the monitor is showing some anomalies. The two things that jump out right away are some colored pixels visible at the extreme right side of the monitor, and some mostly vertical lines at the top of the display, with an area of cycling colors as part of these lines. (Please see the high score screen picture in my last post to see what I am talking about.) Does anyone have any ideas as to how to remedy this? Hopefully it is fixed with an adjustment, as I am not sure I am ready to install a new cap kit.