If you've taken the car to the dealer for any work, like changing the spark plugs (or even having them check the plugs), it might be cracked from the techs. We had a customer with a brand new IX a while back, had some issue with the valves ticking when the car was bone stock. We sent him back to the dealer, and sure enough, the ticking was gone, but the plug wire cover was cracked.

Jerry

 

they will crack very easily if they are overtightened. You MUST tighten them by hand and maybe a half a turn after it is snug. No need for it to be super tight and crack.