That's someone taking the discs out with a tool that doesn't fit and f$%$%d it up and slipped leaving the mark on the face of the action (the line that goes down). The round mark around the disc on the left is from the brace he used. Discs go in at an angle hence it is more marked at the bottom.
The slots on the discs are majorly f%$%$d up.
That is no weld , imo anyways.

Wouldn't be easy to rectify that.
Shady craftsmanship!