I've been working alongside Quaife Engineering in the UK for a while, not on the engineering side though, and always try to push VW ideas through. Speaking with them this week I find out they're in the process of producing a ATB Helical LSD for the 091 box. I've also been told that the more enquires they get about this diff, the quicker it will go into production, so if you're interested give them a call or drop them a line via their website:
http://quaife.co.uk/They have some videos on there too, but my favourite is
http://youtu.be/ZvP9Pe0a9DY
