I had the same problem with a Model 1 kit I assembled. Strangely enough the problem didn't occur until I had at least 500 rounds through it. I too, had the very same marks on the brass.
I found brass shavings wedged in around the ejector which prevented it from springing back and ejecting the casing. Even after cleaning out the area and testing by hand for function, ( as ArmOrdGuy said ) it would fail again on the very next round!
> I cleaned the ejector, bolt and spring. ( Total disassembly. ) Still jammed.
> I tested the spring pressure and finally replaced the spring, even though it didn't seem to need it. Still jammed.
> Changed ammo manufacturer. Still jammed.
> Finally I used very fine sandpaper to smooth the edges of the ejector so there would be less chance of it scraping the brass. That worked!
I concluded that it must have been a combination of the new spring and the deburring/softening of the ejector itself.