Duel push button syphon not working correctly?

I have a similar problem. When you look down the wide pipe [the one that moves up and down to release water into the bowl] a constant trickle of water can be seen as if the seal is not working properly between pipe and ceramic opening to the bowl.
I have felt round both plastic pipe and ceramic lip but can't feel any abrasions. The dual flush has also never worked really well and the best way of operating it is to push both buttons. It's as if it cant dump enough water to create the syphon to pull all the waste throught properly.

pd
December 2009