I to the best of my ability try to drill at the end of the crack and if it should spread further so be it, you've relived the crack and the stress and that little extra crack is now repaired and it's not in the stress area of the windshield, the little crack will probally be invisible compared to the hole you just drilled. fill it to the drilled area and finish the repair thats what I do, I have one just like it in my work van and had been there since thanksgiving and has'nt spread any since the repair, it's been in 40 degree weather and up to 90 so far this year.

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