Starts to have an interest researching old musical (4)

I believe the answer is:

hair

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'old musical' is the definition.
'hair' can be an answer for 'musical' (1960s musical). I am not sure about the 'old' bit.

'starts to have an interest researching' is the wordplay.
'starts to' says to take the initial letters.
The initial letters of 'have an interest researching' is 'HAIR'.

Can you help me to learn more?

(Other definitions for hair that I've seen before include "Whisker" , "Filament growing from the skin" , "Mane" , "Whiskers" , "1960s' rock musical with nudity" .)

I've seen this clue in The Independent.

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