TBF once you open it up you will work out how it all works simple mechanisium pulleys and cogs.
some people find hairs and crap clog up the whole system and all you need to do is clean them up with any lubricant, re-grease the cables and re attach and job done.
If its broken i.e plastic housing for whatever reasons proberly the last butcher, then start looking for a secondhand one.
