I am trying to sort out sister's cold tap which is dripping. Off to get a ceramic insert, duly fitted and hey - no dripping - but the problem is the tap lever itself now wont fit snugly onto the new insert. The problem is the knobbly bit on top of the old one, pictured here

This knobbly bit seems to click into place within the tap lever, but the modern ones dont have this knob. Is it a case of tough - replace the tap - or will there be a merchant somewhere that sells this old design still? Push comes to shove, can I cobble together a solution that would work?
TIA.

This knobbly bit seems to click into place within the tap lever, but the modern ones dont have this knob. Is it a case of tough - replace the tap - or will there be a merchant somewhere that sells this old design still? Push comes to shove, can I cobble together a solution that would work?
TIA.
