On both of my passats, I had a coolant leak from the back of the engine. There's a plastic water outlet bolted to the back side of the cylinder head.
On my 99, a hairline crack opened up on a mold line. This lead to loss of all the coolant with much steam.
On the 2001, the entire plastic housing basically fell apart into pieces.
The fix was to replace the plastic water outlet.
I have the 1.8t though...not the v6.
It wasn't particularly hard to change, although the space to work is kinda tight.
Its held on by two 10mm bolts and various hoses.
First item on this page...and also the coolant sensor plugs into this part too.
Ok..none of this may apply to a v6...but..couldn't hurt to check.