I know people have had varying degrees of success fixing these cracks. I tried and I’m pretty good at that stuff. I even bought the hot stapler that melts wire staples into the plastic, pulled the dash, and used about 50 of those on the underside to fix the 3 cracks- 2 by the airbag and one long one by the instrument cluster. While working on it I noticed the plastic in those areas was darker than the rest. It had “ rivers” of dark plastic where the cracking occurred. I’m not sure if that was a result or cause of the cracking. I also noticed the part that goes between the windshield and dash was brittle and broke in 2 places when I tried to remove it.Drill a tiny hole right at the very end of the crack and epoxy it all back together. I'd suggest the black J-B Weld Plastic Bonder since it matches the factory Ebony dash so well. But if your interior is any other color- good luck!
Fixing the crack and adding support under the center (folded spare rag or towel) will really help to prevent further cracking.
I reinstalled the main dash and ordered the other part. Within a week there was a new long crack near where the other one was by the instrument cluster. And when I pulled that dash again to replace it, I experimented with the different areas. I cut pieces out and played around a bit. That darker plastic snapped super easy, it was real brittle. The rest of it…I could bend it back and forth and couldn’t get it to break, which is what you’d expect of plastic.
So I guess what I’m trying to say is…I don’t think it’s worth trying to repair most of these. My thoughts are that there is some defect in the manufacturing process that created weaker plastic in those areas. That’s the only thing in my mind that could cause the different characteristics of the material. If it was sun doing it, I think the entire dash would be brittle and would break in more areas other than the 2 common ones. Or would be brittle in more areas.
Of course, theses are only the opinions of some guy on the internet so take it as you may. I posted pics of my findings in my build Silverado thread but it was a ways back. I did find the discoloration and brittleness pretty interesting. The top of the dash didn’t show any difference in color or texture. This was the Ebony color so it was black however on the underside it was black and then super black in the brittle areas.