That’s pretty common for the original DC spoilers, it’s hard to find ones that were actually mounted that aren’t like that. You’ve got a pretty clean example there, it looks good.
They were originally supposed to be mounted with plastic push rivets, but they end up getting mounted with sheet metal screws a lot. The bottom of the screw pocket doesn’t always sit flat on the trunk so when the screw gets tightened down the ABS cracks.
An ABS epoxy will take care of that. And if you put spacers on the backside of the screw pockets when you do that it’ll keep it from cracking again.