Please help! Holster leaving strange markings on slide finish (Not usual wear)

[Vaal]

Eezox.

https://www.6mmbr.com/corrosiontest.html

I second that. To "stop" the pitting, use a green plastic pot scourer or fine steel wool lightly with oil on it. But a edc gun is a tool and some wear shows character to me.

[Jof]

My P320SC has the exact same mark in the same spot (a little more pronounced) and I get the same 'oil lines' as described by the OP, even in the cold of winter. I have the same Kydex holster (same manufacturer) for my G19 and I do not get the mark or the 'oil lines'. After this post I will assume it is a 320 thing.

The mark sort of got to a point where it no longer gets worse. I have tried to scrub it with the green scourer but it does nothing. That said, it doesn't really bother me so I ignore it.

I do wipe the firearm at the end of each day, strip and clean once a month if not shot, and apart from the mag release 'button' that continually rusts and needs attention there is no other issues with pitting, rust etc on the rest of the firearm (and I have looked closely)

[A-R]

I second that. To "stop" the pitting, use a green plastic pot scourer or fine steel wool lightly with oil on it. But a edc gun is a tool and some wear shows character to me.

The green plastic pot scourer is a really bad idea to use on gun finishes. It will take normal gun blue right off and leave you with shiny steel.

The Sig may have a somewhat more wear resistant finish, but I still would not chance it.

Fine steel wool soaked in penetrating oil is good if applied lightly. It will remove rust, but not gun blue.

Just fix the cause and prevent further damage. As William Shakespeare said: What's done is done and cannot be undone.