You say Scotchbrite and I immediately think of the pads on the wheels for the diegrinder. (Same material as the pads although not as aggressive) Back about 10 or so years ago GM did a study as to why they were having so many lower end issues. (Bearings and such) most of the lower end failures had a intake revealed and Scotchbrite pads were used for gasket surface cleaning. Immediately, Bristle Disc's were designed and recommended.
I could see that. I used scotchbrite for many years, replacing the failed intake gaskets on the 5.7 Vortecs. But, i would always cover the intake valley and plug the ports. Also vacuum or blow everything out before assembly.
Careless parts changers may be the issue with not protecting the engine internals from abrasives.