Well, I'm actually not sure you have the evidence to support that it stuck

Piston rings rotate to keep from scoring the cylinders and valves rotate or
they would score and burn. If a piece of carbon was under the valve and holding
it partially open it would lower CHT and raise EGT.

If an injector was plugged it would probably go over peak and lower CHT and
lower EGT.

If the injecter was stuck open it would flood and lower CHT and raise EGT,

The reason for raised EGT on this one is the fuel burning in the exhaust
system. This should make the EGT noticably more on this cylinder than the
others.

Life was easy before computers and analyzers. This is an interesting problem
and I swear that I am no expert on this.