The GI M1 Carbine was not without reliability issues:
Forgotten Weapons: KEN HACKATHORN ON THE M1 CARBINE: REPUTATION VS REALITY
And the Universal M1 Carbine late Model has its supporters:
M1 Carbines Incorporated: Post WWII Commercially Manufactured M1 Carbines (U.S.A.)
The dual recoil springs and bolt design seem to be recognized as improvements. The only thing needed for the often criticized late model slide design is "4130 steel heat treated to 35Rc".