if you can get in with a dremel tool and a a small metal cutting wheel cut a slot in the flat and use a small sharp chisel to break the nut, once it breaks it will come off.
alternatively use a product called crc freeze out. it is some fluid that freezes the parts to -20 below zero
and lubricates them.  this stuff is far superior to pb blaster and can be found at your flaps
mike
ps works in 2 to 3 mins

> David,
>
> In almost 45 years of working on cars, I've never had a penetrating
> oil of any kind solve a problem like you are having.
>
> If you have a good nut splitter try that. It has worked on rusted,
> rounded exhaust nuts for me. I have been able to chisel and grind the
> waste nut away and rechase the threads.
>
> Prepare to break the studs if the nut splitter doesn't work.
>
> Jim
>
> On Mon, Feb 8, 2010 at 5:46 PM, David Marshall
> <mailinglist@fastforward.ca> wrote:
> > I am trying to replace the turbo on my Syncro TriStar.=A0 It it held on
> > to the manifold with three 13mm nuts, these nuts go on to studs which go
> > into the manifold.=A0 I really don't want to break the studs.=A0 I
> > can put enough pressure on the socket where I know if I go much further
> > the stud will break.
> >
> > Three days of penetrating oil
> > "3-IN-ONE 'High Performance Penetrant'" and no with luck other
> > than my garage stinks.
> >
> > I've tried the tighten a bit and
> > then loosen which seems to work with allen bolts and light tapping with
> > the impact gun... they're still in place.
> >
> > What should I do
> > next?
> >
> > David Marshall
> > VW Adventure Driver and BMW
> > Adventure Rider
> >
> > HasenWerk
> > http://www.hasenwerk.ca
> >
>
> ------------------------------
>
> End of vanagon Digest - 7 Feb 2010 to 8 Feb 2010 - Special issue (#2010-121)
> ****************************************************************************