You're right Roy, in 14 pages of official F2 manual they don't even mention breathers as far as I can see.
Pictures/ schematic show nothing more than external drainage from float bowl vents, but no specific data about maintenance of the intricacy of anything else.
I worked much more on them when contemporary, so no real need to strip and replace components just setup.
I can see that opinions of these PD series are based on things like this in justification for an awkward reputation, but they are a very good carb design and certainly address their predecessors (which are just essentially run rich to cover design limitations) shortcomings in accurate fuel metering with increased delivery for acceleration phase. They are in reality how an engine should be run efficiently and with power when needed.
Just need very diligent cleaning and setting to fully optimise their metering accuracy.