My sink plug gets stuck. You push it down to plug the sink and push down again to unplug. It does not have an arm system.
It get's stuck when you push it down and you have to pull the drain pipes off and push a screw driver up to push it out.
I have unscrewed the plug and checked the ring seal, it is fine, there is no hair or debris in the drain or around the
mechanism. If you push the mechanism down without the plug on it, it works fine.
It is only about 15 months old and has worked well up until now.