Item 97 on this page Richard
CZA4500, you also need the washer for underneath, CZA4263.

http://www.mgocspares.co.uk/acatalog/MGOC_SPARES_SEALS___FIXINGS__MGB__103.html


DaveW
'05 Red Roadster S1
'16 Yellow (Not the only) Narrow AR GDI Plus 4