Have seen two vanagons so far with the pipe problem you describe - the
metal sleeve slid out about a quarter inch.

each time it was the right hand pipe, the one closer to the passenger's
side of the van.
both times I was able to get a hose over it far enough
to make a good seal.
I was unable to push the metal sleeve back into the plastic pipe,
although i did not try heating it with a heat gun, which might have
helped or ruined the whole pipe !

re rear heater,
don't know if you are the guy who says he has a NEW rear heater, but my
recomendation is to always disconnect the rear heater - they just rot
out.

the only thing that can be done to keep them from corroding and leaking
is to keep them on about 30 % all year so fresh coolant circulates.

I have occasionally run into a situation where you just CAN NOT get the
right part, even tho you have a stock US model.   Mistakes get made, and
parts people can only go with the numbers and pictures they have,
and if it's not in the price sheet, well, it doesn't exist.

  good luck,  hope that helps a little, scott