Steelworker QA guy here: That's a casting mark, not a crack. If you want to be sure you can pick up some penetrant/cleaner/developer and test it. Short instructions on this, spray cleaner, wipe off all crud. spray penetrant wait a few minutes, wipe off as much as you can with lint free rags(bedsheets), wet a rag with the cleaner and wipe it till almost no red is showing up on fresh rags, spray developer wait a few minutes. You won't get all the penetrant off so the developer WILL have red spots, but unless any of the spots grow off the "crack" you're good, if the casting mark turns into a giant red blob you have issues. hers a link to some penetrant thats pretty cheap, I don't use this brand at work but 3-36 is everything WD-40 wishes it was https://www.amazon.com/CRC-Weld-Chec...+penetrant+kit
its got the cleaner and developer tagged as the bought with. Feel free to pm me with further questions.