ok the answer is ........


they have wire in them as all engines are built buy robots and so they need the wire in them to allow the robot to pick them up and place them on the engine

to keep the shape and for the robot to pick it up magnetically

after that they can be made of just rubber but they discovered that garages was turning them back claiming there the INCORECT part as the one they took off as made of rubber and has a wire bead

yes garages are dumb

interesting yet soooo simple,,,, there is NO other reason for this no matter what you are told,,, this is the ONLY reason for it

imagine a robot picking up a bit of rubber,,, simple isnt it