Having looked closer at my oil breather, the external spigots are 23mm o.d. and 24mm o.d. not as stated. But having re-read your earlier post it's the spigot on the cylinder block I should be measuring. I'm hopeful of getting back to Stafford in the first week of March so will measure up then. Does your Mk. 1 solution still use the OE oil breather, or does the block spigot vent straight to the catch tank?