Oiling the tip of a CO2 cartridge

Seasons greetings!

Whenever I replace the CO2 cartridge in one of my guns I always put a drop of oil on the very tip of the cartridge. When I looked down the air chamber of one of my guns today I noticed that the o-ring surrounds the area where the tip is inserted. Should I put a drop of oil on the CO2 cartridge neck also? What method do you use?

Thanks for your advice.