nik take your under tray cover off,mine was found sitting on it,me thinks this is a inherent problem with the compressors,hopefully all youve got to do is the simple fix that alot of us have managed to do,fingers crossed it isnt totally u.s. iirc all it is is a plate that slides on the spline on the compressor,(did you have any noise comming from it???)if not YOU MIGHT BE LUCKEY in the fact that it might of just come off?and not elongated the plate(which mine had)my mechanic also put the newone on with lock tight just to make sure it stayed secure,just remember there isnt much room.