Maintains health of The Castle's leaders frozen in time (5,3)

I believe the answer is:

keeps fit

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'maintains health' is the definition.
I don't know anything about this answer so I can't tell whether this works.

'the castle's leaders frozen in time' is the wordplay.
'the castle's' becomes 'keeps' (I've seen this in other clues**).
'leaders' suggests taking the first letters.
The initial letters of 'frozen in time' is 'fit'.
'keeps'+'fit'='KEEPS FIT'

'of' is the link.

Can you help me to learn more?

I've seen this clue in the Irish Times.

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