Has the horizontal shaft gear (white nylon gear) inside your overlocker failed? Does it look like this?
http://www.sewingpartsonline.com/horizontal-shaft-gear-bernina-bernette-50141103.aspx
My repair man obtained this part from Bernina and was able to repair this although it is a labour intensive repair requiring pulling down the whole machine to do. But the part itself was only $US38.
You can buy from sewingpartsonline as per link above.
Or you could ring Bernina head office in your country and talk to someone about it as I was initially told my machine was unrepairable as this part was not available by a local store who wanted to sell me a new one. I guess in light of the 4-5 hour repair time, this is probably a valid call if you buy a new plastic serger but I love my Bernette and felt it was worth repairing, not junking it. It is now 5 years later and still going strong since that repair. My OSMG (old sewing machine guy) Ken told me that the nylon gears sometimes will just crack, even if the machine hasn't had lots of work, just plastic ageing.
Hope this helps you - please rate me 4 thumbs up if so. Cheers