I think normally the leak is water coming out from cartridge stem (the rod that rotate when you open or close tap). It has nothing to do with the rubber inside the valve which when damage, you cannot closed the water properly thus keep coming out from the tap.

There is an o-ring that seal the water from coming out through the stem. You just need to tighten the small nut that is visible from top (where the stem enter the whole assembly). This will press and expand the o-ring and stop the leak. If too tight, it will be hard for you to turn the tap. So, just tighten it just enough to stop the leak.

Related to my post #17. Yes, open to ma will also press the o-ring inside and may stop the leak too.