The most common and most likely answer to this crossword clue is the 5 letter word QUIFF
I've seen this crossword clue in The Daily Telegraph
Q
U
I
F
F
Buddy explains!
The straight part
We know that "A well-oiled lock" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a well-oiled lock = quiff.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does QUIFF mean?
QUIFF noun- (British dialect) A puff or whiff, especially of tobacco smoke.
- A trick or ploy; a stratagem.
- A hairstyle whereby the forelock is brushed and/or gelled upward, often associated with the styles of the 1950s.
- To arrange (the hair) in such a manner.
- A young girl, especially as promiscuous; a prostitute.
- The vulva or vagina.