Dripping Mini drinking tap

Hello

I have a tap used with a in line water filter. It is of this type

http://www.freshwaterfilter.com/traditional-mini-tap-181-p.asp

I have taken it apart and there is no washer. Just a valve with plastic that rotates 90 degrees to allow water to flow through it. Does anyone know how to repair this, I cannot see a way of taking it apart or is there somewhere I can get a replacement valve for this ?

Thank you Chris

 

That is great Thank you