In reply to bearbreeder:
OK i wrote to them regarding this and they did offer to sell me a new zero for 25 pounds but they said they can't repair the trig wires on the zeros and the trig wires do break pretty easily on these cams IMO.
They claimed the reason why was that they couldn't properly inspect the stem as it is covered in a spring and that they have to ensure the cam is still safe for use whenever they replace trig wires or slings and that they believe it was still be as strong as the rated strength they stamp on the sling.
I wrote back saying I didn't understand the reasoning I mean look at the new heliums they are covered in plastic, you can't inspect the stems on them either (plus lots of other cams are like this some of which I've had reslung in the past). They never replied to that email.
Personally I won't be buying any more zeros until this issue is sorted and I would advise others to do the same. I also can't see a way of home repairing them, in the past I've used fishing line but I can't think of anything that would work well with these cams bar buying a swaging kit capable of swaging very thin wire and I can't be arsed to do that!