[FWB]

when putting holes in plastic care must be taken to not stress the material or it will crack just like you describe. with that being said plowing a drill through a Plexiglas piece takes special care when the drill exits the other side. that is where the stress is greatest.
whether the material is Plexiglas or trade name Lexan is irrelevant,... lexan is Plexiglas...but with optical qualities.

to replace the wings, i would opt for a set made locally, you are more inclined to get better quality. save the old ones for a template. material can be bought through Mcmaster-carr online