Miles,
When I referred to surfaces possibly being unequal, I was mainly referring to the the interior frame surfaces in your picture, the red arrow pointing to a mark.
I see that you are aware of the tape routine at the rear of the Luger. Someone here mentioned such years ago, someone had a piece of brain I reckon, a simple and easily read diagnostic. Every now and then on this forum, there is an elegant piece of information for the shooter that stands out.
A few of us here, have delved more deeply into the Lugers from a mechanical and functional point of view. Not much of a badge of honor or meant as imitation; just that we have the curiosity and are willing to take responsibility for our mistakes in learning on our own. An in the flesh mentor is worth his weight in gold, but not many have that privilege. There is nothing that one cannot learn, if you take the time and effort to do so, by whatever means. Just a bit of encouragement.
From what little I know about the issue you presented, the pictures do not really present much of an issue. A lot of Lugers will give a light touch at the rear, I try to get rid of such myself, with various approaches, but only one opinion in the many. Everyone likes to think for themselves you know.
Some of the rashly purchased Lugers that I got over the years, the first time I put rounds through them, I noticed a sting in the hands from the grip. There were ones with very weak recoil springs; so one might consider using one's sense of touch. If it is just kinda soft recoiling feel during operation, probably all is in pretty good shape. If you get a stinger, something is amiss, possibly the recoil spring or ammo power. The Luger will function for quite a while with a lot of abuse really, for a 100 year old design, tis not so bad. As we get older, we all seem to need an little extra care......
Rick W.