Last letter or letters from some garage (5)
I believe the answer is:
omega
'last letter' is the definition.
(last letter of the Greek alphabet)
'letters from some garage' is the wordplay.
'letters from' says the answer is hidden in the clue (a selection of letters from the clue).
'OMEGA' is hidden in the letters of 'some garage'.
'or' acts as a link.
(Other definitions for omega that I've seen before include "Greek character symbolizing resistance" , "16 letter" , "Final outcome" , "Last thing" , "letter from abroad" .)