An analogy:
My car is ancient but a good, reliable runner. When it's due for its MOT, I put it into my local garage for pre-MOT assessment with the instruction: "If the cost of the repair is less than what it would cost me to buy another reliable car, go ahead and do it".
So I suggest that you adopt a similar approach:
If the van is reliable, work out what it would cost you to replace it with an equally reliable van (in the same general condition). i.e. take the cost of a replacement van and subtract what you'd get as the scrap value of your old one. If that exceeds the cost of fixing your old van, then fixing the old one is the option you should go for (as, either way, you'll end up with something very similar).
However if your old van is already unreliable (or you know that it would cost a massive amount to get it through its next MOT), then take the opportunity to ditch it and get something better now.