This happened to me last year and I repaired it using windshield urethane as well and it has worked very well! Mine tore because the rubber attachment tabs had popped out of place in that corner and the window actually stretched it to the point of tearing while being rolled up. Make sure after your repair, that you check this and see if it needs to be pushed/tucked back in all the way so it's snug or else next time you roll up your window, it just going to tear again! Don't ask me how I know this.