You need to get hoses rated for R134a. The molecules are different sizes and the tolerances that would hold the larger R12 molecules in don't hold the smaller R134a molecules and they seep out. Take a look and see if you can find any Gen II minivans in your local junkyard (1991-1995) with the 2.5. I wouldn't be surprised at all if the hoses for a later van would fit yours. The changes to the vans were more evolutionary than anything (aside from styling) from Gen I to Gen II from what I understand. The Nippondenso compressor that you probably have (10PA17, may have a suffix, i.e. A,B,C) was extremely common on the K-based cars, so something from, say, a '94 AA or AP, which are still pretty common, might work, and would be already set up for R134a.