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Hallo Theo,
my answer
a.) The length of my fly has been estimated to be 23 mm from head to wingtip
b.) In the eye you can see a bandage at high magnification. ( see photo)
c.) Tabanus bromius --> length 11,5 mm bis 19,5 mm (Wikipedia)

Theo, is the name Tabanus bromius??

Viele Grüße,
Klaus