How to fix my mixer tap ?

Hi, I have mono block mixer taps and water is seeping from the stem above the taps, undone the circular nut which then exposes a plastic cir clip and below this is the rubber ore ring which is worn, I can take the cir clip off but can`t slide the rubber off or the nut as the tap has a flange at the spout end wider,I see no grub screw, have turned 90 deg,the stem lifts slightly but won`t come off afraid I might break it if I pull too hard, tried tapping when pulling to no avail, the water is quite soft so not suspecting lime scale, help please. Sorry not sure of make as were installed when I moved in the house. Regards.