I had the same problem on my 16v, tried everything on the nut and shock but no joy.
I ended up covering the engine and grinding off the flat ring of the top cap,
It's shaped like an upside down top hat, I ground off the brim!
The strut will then drop through the hole in the chassis leg and you can get it in the vice etc,
A new top cap from VW was about 7 quid
Just make sure you cover the engine with something flame retardent, especially the metering head