I own two MAC-90s with the "toilet seat" stocks and both of them broke in exactly the same place, upper left where it meets the receiver.
They are unquestionably the worst stock ever put on any rifle ever made. They are also not cut for ambidextrious use and are uncomfortable for anyone who shoots left handed.
I couldn't get rid of mine fast enough. I did buy two replacements (cheap, new removals) to be installed if I ever sell the guns, just to bring them back to original (**** poor design) condition for someone who wants and original gun instead of a functional reliable stock.
Bottom line.......they suck and diminished the quality of what is actually a great gun, simply to placate the ignoramuses in the business of the gun control agenda by making a useless cosmetic change so they could "feel good" about doing something.