Carb to head rubbers

[jason1]

Hi all , need some rubber advice  :eek  . Mine are cracked and wondering if there are easy signs to show there leaking ? My fazer does use a lot of fuel , even just cruising = 120 to tank . I have sprayed rubbers with wd40 when engine is running and cant see any bubbles but you can see movement in the cracks from engine vibs .
  Also how easy are they to replace ? is there any probs foccers have come across ?
Any info will be great