You need(ed) to stop drill the end of the crack (or now cracks) to stop the further spread of the cracks. I've used a 3/32" bit for this purpose, but 1/8" would probably work as well. By "rounding" the end of the crack, it stops the propagation.
Then, you can fill the crack and the stop drilled hole with a suitable filler such as Lexel caulk. You could also tape over it with Eternabond tape.
Hi-Lo 1707T - Tire Minder TPMS on Tow Vehicle and Trailer, 300W Solar Battery Charger, Equal-i-zer WDH
2014 F150 Platinum 4x4 3.5L EcoBoost SCrew