> Well, it's leaking from somewhere!

That's for sure!  With 134a and some dye in the system,
I don't see why a good shop can't find the leak.  But they
have to check everywhere, including up the pillar and
to the evaporator, not just the engine compartment and
under the van.

As far as hoses are concerned, I converted my '87 five
years after I bought it with no cool air from the AC
to 134a.  The shop tested with Freon, found no leaks,
evacuated and charged with 134a.  It worked perfectly
for several years with the VW compressor and then with
the Subaru compressor until the Subaru compressor self-
destructed.  Their observation was that old hoses
didn't leak 134a, smaller molecules not withstanding,
because the old hoses were saturated with the oil which
sealed them.

YMMV, but I wouldn't throw money at it.  I'd try to
find the leak and fix that.

Richard