[Username1]

Could be a cap, buffer, transistor. Does this monitor only handle one kind of signal, I'm assuming its not multi-sync. You may have to get a schematic, and trace through the sync from the input to the horiz ocs, to see where the sync is falling, and why it seems to be in the wrong spot causing the image to shift.

There is a phase shift through a cap,
there is a phase shift through an inverter,
and if a buffer stage is bad it could cause a late trigger.

There are a few possibilities.

Time to get out a schematic, and a scope.
Take a long look around inside for any physically bad looking parts, like caps, IC's with a hole or a part of it chipped off from overheating, parts running too hot.

My tv instructor use to say "look for the part with the green arrow pointing to it."
He liked being a smart-ass..... I get a little of that from him...