Page Finn spoilt, leaving a bit of a mark (7)

I believe the answer is:

pfennig

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'bit of a mark' is the definition.
('pfennig' is part of 'mark')

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for pfennig that I've seen before include "Old German coin" , "Old German currency unit" , "Former German coin" , "One / One-hundredth of a Deutschmark" , "old rhino" .)

I've seen this clue in The Telegraph.

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