"Viperdoc" wrote
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.

The odds of two clean looking plugs both being bad are low. The odds
that an injector with a visible hole was bad enough to shut down a jug
are also low. Likely something else is going on.

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

You should stock some spare rocker arm cover gaskets.

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

Could be anything. Stuck valve, plugged injector, bad plugs (I have
had both plugs go bad on one jug), bad cam lobe - anything.

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

First off, every time I've ever had an engine problem my mechanic has
always said stuck valve. Know how many actual stuck valves I have
had? None. In any case, if you really don't want to pull the rocker
arm cover, get a flashlight and pull the prop through. You should be
able to shine the flashlight in one spark plug hole, and look through
the other (may need a mirror) to see the vlaves move as you pull the
prop through. If they open and close, it's not a stuck valve. If a
valve is stuck open, well, there you go. Do the rope trick and use
some Marvel Mystery Oil.

If it's not a stuck valve, you will have to pull the rocker arm cover.
If you damage the gasket, it can be repaired with red (high temp)
RTV, at least as a temporary measure. Make sure you have full travel
on the valves - that will eliminate the cam.

Michael