Why? has it chewed the cable?
if it has before you look at repairing this window reg you need to take a look inside the motor where the cables are rolled up, inside there there will be a plastic threaded type wheel which turns and winds each cable [depending on where window is up or down] into the groves of the thread in this wheel as it turns, when the cable breaks or becomes slack they tend to "jump" threads, when this happens they get caught and the result is like a cross threded bolt, it destroys the plastic threaded groves that they run in, if you put a new cable on the knackerd threaded wheel it will do the same thing again to your new cable, chew it up or brake a plastic cable mount, they have to sit neatly in the groves, if not bin it and ebay another one.
I have a Meg 2 CC that seems to love eating passenger rear quater lite regs I am on it's 3rd now in 10 months, I was talking to a gut on ebay that seels cables but took it no further as my threaded wheels where no good to damaged to work , sos best get a look at this wheel 1st.
