It's annoying though, because of how long it has obviously been left like that, with crap getting into the system, which has taken me quite a while to flush out (with one of the jets apparently being beyond saving!)
Anyway, according to service.citroen, mine needs part number 643230
Cheap enough from Citroen but I hate my local dealer, because they're a Vauxhall dealer and bloody useless at Citroen stuff, so I ordered it off ebay.
64320 looks like this;
This matches the drawing on service/citroen
It doesn't fit my car, which has this type;

Having another search round on ebay this one looks like the right part, but it says it's for a C1;
Just want to check, does anyone know if this is still the right size for a C5 washer bottle?
Anyone else come across the flap on their C5 being one of these instead of 64320?