My AR was greased with factory brown gunk.
1- I took the handguards, grip and stock off.
2- Sprayed generous amounts of Spray-9 (Canadian Tire)
3- Wiped clean
4- Heated metal parts with heat gun
5- Applied Froglube paste (not their liquid)
Since then, I've fired about 1500 rounds of factory ammo and reloads. I ran a snake bore down the barrel a few times and fully cleaned it twice. I've yet to experience a failure to feed, fire or eject.