If you want to run an AR hard you grease it just like a M1 or M14.
Use a high temperature bearing grease or something similar that doesn't break down at normal AR operating temperatures.
There are higher-tech solutions to the problem, like XF-7, but any high temp bearing grease that's not loaded with PTFE should do the trick.
Just like the high temp greases, Mobil 1 synthetic won't break down at AR operating temperatures, but just like other relatively low viscosity lubricants it can run off if left in the safe for any length of time.
Light oils work well for light shooting and they're cheap and readily available. That said, the high temp greases work better for heavier firing schedules and lubricants like XF-7 don't attract dust and grit if applied as directed.