Packing nut on steering and reverse cable keep breaking

[twosheatoo]

PLEASE HELP - I have 2 2004 Seadoo GTX 185 hp supercharged waverunners. I have now had both of them break the head off of the packing nut that seals the reverse cable and the steering cable. one of each on either boat has now broken. it is a plastic part. does anybody know why and then is there a better fix than putting a plastic nut back into the boat?

thanks,
Mike