is my monitor pooched?

It's difficult to say without actually getting inside it as you can
appreciate, you've certainly confirmed it is the monitor by trying a
replacement.

Several things could produced the fault you described, ranging from
what we call 'dry joint', as you know solder is soft lead, as part's
heat up and cool down this causes stree around the soldered joint and
.. 'hey presto' sometime sooner or later you'll get a bad connection -
that's a dry joint.

It could also be components failure and it is impossible to guess, we
need to know if it's in the power stage, the line output stage... or
wherever and for this you'll need test equipment.

There are high voltages in a TV or monitor - so don't go fiddling
inside

- remember [b:015f731a8f] it's the volts that
jolt and the mills that kill..![/b:015f731a8f] -
mills being the current measured in milli amps, 0.001 Amp.

Davy