[Dukedesmo]

I have seen two types; one made of plastic with an alloy 'ring' around it - these tend to leak around the alloy apart, the other is completely plastic.

The old plastic/alloy type have holes around the base for a 'C' spanner whilst the plastic type have flats on them for a spanner but you may need a hammer and drift to remove as they can be tight (and may be loctited/threebonded in).

Shouldn't break and drop inside and it isn't just a straight hole anyway - there is a kind of 'shelf' but even if it snapped off you could cut the plastic part out easily enough - although you would obviously need a new breather...