Lately I've recently been paying more attention to my M1 Carbines and so watched this nice video on the Forgotten Weapons YouTube channel with Ken Hackathorn discussing the M1 Carbine:
I have NOWHERE near as much as experience as Mr. Hackathorn, but I’ve owned several M1 Carbines since the 1980s and my experience matches his when it comes to ensuring reliability.
My first Carbine was a commercial copy by Iver Johnson, purchased new. It had a problem with an improperly hardened bolt. The locking lugs peened and it had to go back to the factory for repair. I got rid of it a little while after I got it back from IJ.
Since then, I've owned a few USGI Carbines: 1943 Underwood, a 1944 Underwood, and a 1944 Rock Ola. I still have the '43 Underwood and the Rock Ola. On all of them I replaced the recoil springs with new springs from Wolff.
In my experience, the USGI Carbines have been very reliable as long as they were kept clean, lubed, and fed good ammo. The only time I had significant reliability issues was when shooting steel cased Wolf (Tula). The steel cases don't obturate as well as brass and the chamber got filthy. After shooting a box of that stuff I changed over to some RA 52 Ball and got extraction problems. Cleaning the chamber fixed that.
Good .30 Carbine ammo that I've shot includes RA 52 Ball (Remington from 1952), Winchester FMJ, Remington FMJ and JSP, Prvi Partizan FMJ, and Federal FMJ and JSP. I recently got a 1080 round can of mid-1980s vintage Korean milsurp ball made by PMC, and I'm sure that will be perfectly fine.
Finally, if you're interested in keeping an M1 Carbine around for more than just casual use, get ahold of Jerry Kuhnhausen's The U.S. 30 Caliber Gas Operated Carbines: A Shop Manual. It's the definitive work on gunsmithing M1 Carbines.