Old record thus maintained principally in horse racing venue (5)
I believe the answer is:
epsom
'racing venue' is the definition.
(I've seen this before)
'old record thus maintained principally' is the wordplay.
'old record' becomes 'EP' (abbreviation for extended play record).
'thus' becomes 'so' (synonyms).
'principally' suggests taking the first letters.
The first letter of 'maintained' is 'm'.
'ep'+'so'+'m'='EPSOM'
'in horse' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for epsom that I've seen before include "- Salts are a purgative" , "Home to the Derby and the Oakes" , "Location of English Derby" , "can have horses" , "Derby racecourse - salts" .)