I will have a look. There is a slim chance I still have one after my front bumper was replaced, there was something left in a box but can't remember what it was!
I know I have a cap in Agate grey somewhere if that's of use, would need spraying to the correct colour.
EDIT:
This is the part I have 4D0955101A - Pressure cylinder for headlight washer as shown in the photos attached.
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Cars...
'93 Audi Coupe 2.0 Alpine White (sold)
'99 Audi S4 Merlin Purple - K04 upgrade to 412hp (sold)
'00 Audi S8 Agate Grey (Sold
)
'11 Audi Q7 4.2tdi Unknown Red (Classic Red Pearl Effect - thanks MJ)