OK, just finished replacing the caps, still get the same "double image". Anyone have any suggestions?
It's a stable image, I know the game board works, and that the syncs are hooked up properly, as shown:

...with H and V joined together. The game board is a neo geo MVS, which is negative composite sync. I also had the exact same problem when I hooked up a Jamma game (which also was neg comp sync), so I'm pretty sure the problem has to do with the monitor.
I haven't loosened off the yoke, or played with the purity settings. This isn't a purity thing is it?