Sounds like milker might leak. OMG! (4,3)
I believe the answer is:
holy cow
'milker might leak omg' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'sounds like' is the wordplay.
I cannot really see how this works, but
'like' could be 'ly' (similar in meaning) and 'ly' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for holy cow that I've seen before include "Blimey!" , "The goodness" .)