Go Wing or No wing on a 72 Demon 340

How about a ducktail Direct Connection Style Spoiler

Impossible to find and look really good on a Duster, Demon & Dart Sport. My '74 Duster(now a '71 clone) has/had one on it but it's split in multiple places because a kid climbed all over the back of the car years ago.

If I could figure out how to fix it permanently, I'd put it on the car again. But I tried plastic welding it, tried fiberglassing it, every time it didn't last and the cracks emerged again.