When I had this problem, I contacted Sottini UK, the manufacturer.
My mechanism had two pushbuttons sitting in a circular metal housing. To free the lid the two buttons had to be removed thus:
Depress one button. This leaves a space allowing the other button to be levered or eased upwards by a finger, so that the button can be removed along with a long thin plastic stick. Then remove the second button. In the botton of the recess you will see the slotted head of a screw. If it is plastic, be careful to use a suitably sized screwdriver - one that's too small may damage the slot. Unscrewing allows the housing to be withdrawn and the lid to be lifted.
Your leak is likely to originate in the delivery valve diaphragm (at the top of the inlet tube) which should be replaced (cost about 50p).
Getting the lid back on proved more awkward than getting it off.
James Campbell, November 2007
