Foreword: This was the only living forum about the Starex i could find, so i registered, despite my poor knowledge of German. Google translate is my friend, but it struggles with technical terms... So i'll write in English, and i'd really appreciate if you could answer in English. But if i ask something that was previously discussed, please feel free to link the thread, i'll do my best to understand it...
So, Hello Forum! :) a few weeks ago i recieved a 'new' company car, a Starex. First registered in Austria in 2007, 78.000 kms in clock, nearly no rust, overall in good condition, after checking it from the bottom, i would say it wasn't really used off-road. Fun thing, it is a 9 seater, probably hacked with the front-right bench of the 2wd H-1. Most of my questions will be about parts compatibility, as Starexes are rare around here, and factory parts seems to cost a lot... For example when i recieved it, the four wheel drive system was out of order, as this vacuum-membrane actuator failed. The factory part would cost ~€300 and i would have to wait for it for a week. With a talented mechanic, we could fit in the Mitsubishi L200's which is readily available as aftermarket part for ~€40...
You're right, this is the only living Starex-Forum in the net, but there is also a facebook-group. Though I don't use FB I don't know how useful that group might be for you.
For your problem - it's a known issue that the 4wd-insertion of the Starex causes problems. The first and most common breakpoint are the vacuumtubes near the electric valves (you'll find them under the airfilter-case). Depending on time and bad qualitity of the original material used by Hyundai, they mostly have small fractures and should be changed. This can bei done also at home in an hour's work by yourself. For replacement you can use tubes with the same diameter which you get at the car-accessory dealers.