Across:
   1. Remnant vegetation (50%) is scattered (7)
   5. P.S. To fly off? (6)
   8. Recited fluently without repetition for a good mark (6)
   9. The latter part of their rant about it was tiresome (8)
  10,11. Wild ride atop 'Caviar' across the North of Melbourne (8 6)
  12. Being impressed, perhaps, with genre label (5)
  13. Draining workout for pet in gym (8)
  16. Some quite particular canines - the very best were itchy to get even (3-5)
  18. A nation, when a nation loses its ancient leaders (5)
  20. Songs contain note of testaments to 1 down (6)
  23. Historic vehicle track in Eastern Melbourne (4 4)
  24. Treatment of secret "Double 0" characters (8)
  25,17 dn. AC-DC song found at the bottom of the well? (4 2 3 4)
  26. Deceased territory contained (6)
  27. Grave crime of the head: thought and logic! (7)
Down:
   1. State before party - without a target 'score'? (9)
   2. Dead set out! (7)
   3. Get involved before English reinvent letters (9)
   4. Swirling breeze hits latte strip in the middle of Melbourne (9 6)
   5. Dispossess drag (5)
   6,19. Dozen farty rigs befouled Melbourne park... (7 7)
   7. ...as is the way in a big city (5)
  14. Beg for help and an overhaul (9)
  15. Serve heart in country ribcage of foliage (9)
  17. see 26 ac.
  19. see 6 dn.
  21. Row retreats, running through Southern Melbourne (5)
  22. Perhaps football's second facility by the 21 (5)