flush it out real good and use water only... get the temp up to 200 or a little higher like its about to overheat. the reason to do that is it will open the crack real good. if it stops the leak, it will prob. never leak again unless you get it hotter than when you made this repair. there are many products with many issues. this works really well and last. Buy this !
https://www.jegs.com/i/Moroso/710/3...=4579878248437694&utm_content=Moroso 
I use to cut a peice of cardboard to put over radiator then get temp as said to almost overheat condtion . I had a 440 with no issues until I blew a hose one day and overheated. Then I had to repeat the process with great sucess. My opinion is you dont need much stop leak (I used Porter seal) to fix it . Dont fill your motor with to much pellets JMO
