Here's a WAG for conversation's sake. Is the EGT temp low on initial
start up / warm up, while operating at low rpms and or does it cool
down faster than the others on shut down?

Could the exhaust valve be sticking when cold, moving and wearing the
guide in the boss, causing increased oil usage and both aluminum and
steel in your samples yet showing good compressions after warming up?

Like I said, completely a WAG.

If you really suspect the cylinder, I would not fear pulling it for a
thorough inspection. You'd get immediate knowledge of the condition
of the piston and pin, the ability to examine the cylinder, the valves/
seats/guides, and check the rings, and even a peak at a few of the cam
lobes. A wealth of knowledge available for relatively minor $. I've
only had the need and the experience of pulling one cylinder, but
under an A&P's guidance I removed it myself in less than 2 hours and
we reinstalled it together in about 3 hours.

Easier and cheaper to catch a problem before it becomes a disaster.