Oral massage perfect, but not entirely necessary (7)

I believe the answer is:

needful

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'not entirely necessary' is the definition.
'needful' can be an answer for 'necessary' (similar in meaning). I'm not sure about the 'not entirely' bit.

'oral massage perfect' is the wordplay.
'oral' shows a homophone (sound like) (how it sounds when spoken).
'massage' becomes 'knead' (synonyms).
'perfect' becomes 'ful' (I can't explain this - if you can you should believe this answer much more).
'knead' sounds like 'need'.
'need'+'ful'='NEEDFUL'

'but' acts as a link.

Can you help me to learn more?

(Other definitions for needful that I've seen before include "Poverty-stricken" , "Required" , "Nude elf (anag.)" , "Indispensable" , "Requisite, necessary" .)

I've seen this clue in The Independent.

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