Jekyll's replacement, quiet life-preserver in London area (4,4)
I believe the answer is:
hyde park
'london area' is the definition.
(park in London)
'jekyll's replacement quiet life-preserver' is the wordplay.
'jekyll's replacement' becomes 'hyde' (I am not sure about this - if you are sure you should believe this answer much more).
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'life preserver' becomes 'ark' (Noah's Ark preserved life in the Bible).
'hyde'+'p'+'ark'='HYDE PARK'
'in' is the link.
Can you help me to learn more?
(Other definitions for hyde park that I've seen before include "Open area in London" , "capital grassland" , "place of recreation" , "London green space" , "Public open space in Central London" .)