I took the liberty of checking ETKA.  The parts are as such:
025 121 171 is a flange and pipe combination.
025 121 160 D is JUST a flange.

They also do not fit in the same place :)

I don't know the composition of these things.  025 121 171 doesn't
list as being superseded by any other part number, so I'd use the
original part.

-Jason

On Mon, Jul 16, 2007 at 05:02:38PM -0400, TJ Hemrick wrote:
>  OK, here's a stumper for ya.  I'm looking up parts for a customers
>  car.  My dad taught me well and said, NEVER go to the parts store
>  without the old part.  So being a good boy, I take the part home
>  (luckily VW put the number on it) and put in the computer (Site 1) and
>  out pops this:  025121171   Coolant Flange   Metal elbow/flange on
>  passenger side of engine block (attaches to coolant hose). Also
>  replaces plastic version.    So I start digging around a different web
>  site (Site 2) and I come across this: 025121160D  86-92 2.1l Vanagon
>  Coolant Hose Flange for Passenger Side Head (2.1l) Metal.  This is
>  the coolant hose flange that is on the passenger side head on a 2.1l
>  Vanagon (syncro too) right by the power steering pump. It is number 41
>  on the coolant hose chart. The original one may be plastic but this
>  new one is metal.    Now at first glance, I know your saying, "Duh,
>  the part numbers are different" but theirs a little voice in your head
>  saying, hmnnn, the descriptions are the same and the location
>  matches....  So, I do a cross check of the same numbers on both web
>  sites:
>
>  Site one 025121160D  Coolant Flange  Right Head, 2.1L Vanagon
>  Site two 025121171     83-85 1.9l Vanagon   Small Coolant pipe between
>  block and short hose for 83.5-91 Vanagon.  Small Coolant pipe between
>  block and short hose on passenger side of engine.
>
>  Now, that last entry does have some discrepancies (83-85 or 83.5-91?
>  and how could it be 1.9 and be for a 91?)  Regardless, they appear to
>  be the same flange for the cooling system but part numbers are
>  different but items SEEM to be the same.  I don't have EKTA but don't
>  know if it will help.  This is NOT about pitting these two sites
>  against each other.  So don't even go there!  Aside from a simple typo
>  in the last entry to make things extra hard to sort out, does ANYONE
>  know what the difference is?  Yes, their is a substantial difference
>  in price.   Ben, Ron, Frank, Benny (CA), Ken, and a few others in the
>  business whom I've forgotten your names, got any input?  BTW van in
>  the shop that needs it is a 91.
>
>  Thanks,
>
>  TJ
>
>  87 Syncro
>  87 Wolfie