Keith,

I'm not the expert on this but I'll tell you what I think :)

First, it would be good to have the model before it was subdivided so I could experiment with the structure. Not having that, I rendered the subdivided model:



I think the issue is caused by the roof line at the top of the windshield (top arrow) being pulled way back.



If there was an additional Split added on the door (at bottom arrow), and the split at the roof (top arrow) were not pulled back so far, I think it would render fine. My basic structure (before refining) is below:



Ed Ferguson