Hi Inja.... Welcome to Milsurps

What serial range is it ?
Is this a Detachable Spring tube ? Hole drilled completely thru for the Op Slide stop pin ?
Could you post a few more pictures..... 1 of the top of the Slide rail ledge and 1 showing under the slide rail with the stock removed ?

Then maybe 1 more with the crack highlighted with chalk or something so we can better see the extent of it.
Currently... For me, It's hard to make out how far and direction of the crack.

Thx,