Slip into Ferrari every so often (3)
I believe the answer is:
err
'slip' is the definition.
(to err is to make an error)
'ferrari every so often' is the wordplay.
'every so often' means one should take alternating letters.
The alternating letters of 'ferrari' are 'ERR'.
'into' is the link.
(Other definitions for err that I've seen before include "Sin" , "Miss the mark" , "Make a wrong move" , "'To . . . is human, to forgive divine'" , "'to... is human,to forgive divine'" .)