Whats the mark on the cartridge slot and is it something to worry about?

So this is my 3DS from the early 2010’s and it now has battery issues and charging port issues for years

I am buying a new charging port, replacing it and soldering it back on soon.

Also buying a new battery aswell.

Obviously as you can see i’ve opened it up and theres this kind of marking on the cartridge slot and I don’t know what it is and is probably caused by the age of my DS. But is this something to worry about at all? What is it specifically?