Anywhere there's friction
Around the nozzle in the BBU (blowback unit -> under the slide, when you remove it, under the rear sight. You'll see a polymer cylinder that can move back and forth. Best is to disassemble it when you are comfortable enough)
Ideally, clean with Q-Tip and small dab of oil before reapplying new oil, after every shooting session. Clean barrel with cotton patch; Someone else might chime in about using oil or not in barrel, I'm not too sure about this.
Originally Posted by Brian McIlmoyle
Real life comparison,
GBBR- bang bang -- Giggle
AEG-- merrrzip merrzip -- meh