Sink Tap drip

[Paul1]

Does anybody know what the O ring is for at the base of the tap, because on mine it does not come into contact with the bottom of the tube and water runs out at the base of the tap. Its quite easy to pull the tap off and put the O ring further up but when I push the tap back on it just pushes the O ring back where it was. It seems that the tap needs a hard push to overcome the O ring but I fear I will break the base of the tap in doing that because it does not want to push any further. When the tap is pulled off it reveals base is threaded but the tap just loosely pushes on. Looks a poor design, even if water tight water stays in the tube after turning off and if not used for a while can go stagnant because it cant drain out. Because of this I am reluctant to sealant it on. Paul 1.