Leaky methven basin mono tap

Hi,

Methven mono lever basin tap, ceramic catridge has square lever at the top, no splines. vented cylinder, so mains pressure cold and hot.

So our bathroom basin tap has a slow leak after less than 3 years use :/ It appears to be coming up through the cartride housing where the lever is.

Have carefully inspected aand cleaned catridge, no cracks or otherwise visibly damaged parts. All seal rings still appear to be rubbery and havent gone all brittle.

Local central heating place doesnt't stock any 3rd party cartridges that are similar in design. So much for for the wonders of non leaking ceramics, which cost a fortune !

Spent ages googling methven trying to find my model, cannot find exact model. its a square edge design, which is pretty pants because the spout isnt angled, nor the handle so water collects rather than run off. Emailed methven customer support. No reply.

Any advice , do any plumbers stock these original catridges ? I'm located in Colchester.