Wow, I feel your pain and frustration. Talking about a clean break, it's hard to believe that a board could break in two like that. It looks like it was cut in half by a saw.
I have no idea what the normal materials lay up looks like on that board, but it looks like there isn't much there. Guys that build or repair boards will have better insight to what happened. The 380's are not light weight boards, so you would think that they would be stronger.
While Starboard may not want to deal with this issue because of the expired warranty, someone with expert knowledge needs to take a close look at the board to see what happened. If Cobra left out a layer or two of material (no idea if this is the problem), you shouldn't get stuck with a broken board, warranty or not.
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.