I am going through this now.  You don't say what year Vanagon but mine is a 90 and there are 2 part numbers available.  The part I got fits the tank but the 2 wire plug is different.  Probes look different too. I am going to figure out it the sensor will work and if it does may just reshape the very top of this housing to accept the 2 wire quick connect plug.  I think there was some miscommunication on the dealer's part when they ordered the sensor--they had me take it off physically so they could check the existing p.n. Or, it could have been my gasp as they quoted my $65 for the part, I told them the quote the day before was $25 so they may have ordered me the less expensive solution.
  Meanwhile, my cracked coolant level sensor housing has been held together with epoxy plastic weld and filled with epoxy putty.  I was 100 miles from home on a weekend with the family when this happened and the epoxy saved me.  I thought about JB Weld, but it doesn't list plastic repair.

  Chris C
  90mv

John Drew <john.p.drew@GMAIL.COM> wrote:
  Hi again:
So it turns out that the coolant reservoir (not the one behind the plate)
is leaking from the top, and not from below the top pressure cap but out of
the place where the sensor is located- does this mean i need to replace the
sensor mechanism or is it possible that it just needs to be fastened more
securely into the tank? I have yet to disconnect all the hoses and try to
pull the entire reservoir out to inspect it further- thoughts? As always,
many thanks for your feedback.
- the border stories team