To get the latest geberit fill valve in to a slim cistern - disassemble and remove the part with "ears" that makes it too fat for the cistern width - then reassemble. Use the clip from the old fill valve to reattach.
For some reason I went to Roca for a part rather than straight to [email protected]
Roca took ages to get back, so I eventually got the bits off toiletspares by which time cust was getting mardy. Flush valve arrived, went to fit and the cradle was brittle and it broke when i was putting the valve in which is unusual and was not exactly what i hoped for.