The good news is that the height seems to be unaffected -- this means that you don't have a flyback problem. If the flyback were bad, the HV would be affected, which would change all dimensions (as well as brightness and focus).

The likelihood is high that the problem is localized to the horizontal deflection coil and associated connections. I'd look very carefully at the connector, especially where it's mounted on the PC board. Since the drive for the deflection coil also comes from the flyback, check the connections there, too. Even if you can't see anything obviously cracked, freshen up all of those solder connections (with fresh solder, of course). Can't hurt, and quite possibly could help.

Just don't work on the thing with the power cord plugged in and you'll be fine. [i know you know that, but it never hurts to get a reminder.]