The most common and most likely answer to this crossword clue is the 4 letter word PEES
I've seen this crossword clue in Financial Times
P
E
E
S
Buddy explains!

The straight part
We know that "Leaks" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case leaks = pees.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 PEES mean?
PEES noun- Urine.
- To urinate.
- (mildly vulgar) To drizzle.
- The name of the Latin-script letter P.
- The bill of an anchor.
- The sliding weight on a steelyard.