Bleed the system. Turn lock to lock and reservior cap opened. I generally keep doing partial fluid replacement from time to time by sucking out fluid from reservoir..it keeps the system noise free and is very easy to do as compare to taking the pipes off which create a big mess.
Replacement is cheap, i replaced one on my city (same pump) 2 years ago for 2500/- its working fine uptill now. Usually when the pump is really starting to fail, it will give a faint tuk tuk noise like those water sucking machines make. I kept driving in that condition for 3,4 months until the noise became more prominent and one day the pump failed completely vomiting oil all over.. took off the belt and had the pump replaced.
Wait for the tuk tuk noise ... thats when you really need to replace the pump. meanwhile replace the oil, fix the leaks and keep the system ncie and clean.