I am glad to report that the gun is now fixed. Recoil spring was worn out, and changing the spring improved things a little but ejection angle was still not right. Ejector was attended to by an experienced tinkerer and now cases eject as they should.
I failed to see any fault in the ejector: bluing remained so I thought it can't be worn but I guess it was, or maybe there's some wear in other places that necessitates ejector adjustments. Anyway, most of you were absolutely spot-on in your replies! Thank you all, especially Walt Welch for taking the time to mail me.