Stuck valve versus plugged injector

My AEIO 540 equipped plane had a cylinder stop working following a flight
yesterday. It ran fine during the flight, and quit on the taxi back to the
hangar. (Number 3)

It started to run rough, and a mag check showed that the cylinder was cold
on both (six probe EGT and CHT).

The plugs both look good- not shorted or oil covered or bashed apart. I
pulled the injector and at least could see light through the orifice, and it
is currently soaking overnight in solvent.

I don't have an extra valve cover gasket, so I'm a little leary about
pulling off the valve cover.

Anyway, do these symptoms sound like a plugged injector, stuck valve (only
260 tt on the engine), or something else?

Any other ideas?

My mechanic is talking stuck valve, but how do you distinguish this from
something else?

Anyway, he's coming to take a look next week, but if I can solve the problem
in the meantime it would sure be nice, since it looks like good flying
weather this weekend.

TIA

JN