[blykins]

That's a new one for me. Never seen anything like that.

I've heard of guys having a microscopically incorrect surface finish on the valve stems that acted like a file over time, but I've never seen that before.

I also know that GM had a batch of bronze valve guides that were incorrectly hardened on the Z06 Vette several years back. It accelerated the wear.

I'd change the guides and valves both. It will need a valve job as I imagine the valve head has been dancing around on the seat.