Presidential name on a manuscript (5)

I believe the answer is:

adams

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'presidential name' is the definition.
(I've seen this in another clue)

'on a manuscript' is the wordplay.
'on' is a charade indicator (letters next to each other).
'manuscript' becomes 'dams' (I can't justify this - if you can you should believe this answer much more).
'a'+'dams' is 'ADAMS'.

Can you help me to learn more?

(Other definitions for adams that I've seen before include "Second and sixth US president" , "Sort of apple" , "Douglas - (The Hitchhiker's Guide to the Galaxy)" , "Ansel --, US landscape photographer" , "Former US president" .)

I've seen this clue in the Evening Standard.

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