I'd add these on to the list:
- HPI check for mileage and title,
- V5 log book or what ever its called now
- good service history (with invoices preferably as service books are not difficult to fake)
- evidence of any accident damage - look along the length of the van for dents, check the shut lines around the doors are even - ie not 10mm on the top and 1mm on the bottom
- Steering 'clonk' - there are several threads about this on the forum.
- What sort of driving has it done - lots of motorway work (good) or just driving around in town (no so good imho)
- Press EVERY button and twist every knob (might take you a while in a 'velle ). Make sure the a/c works and pumps out cold air.
- If possible, speak to the previous owner (name and address from the V5)
- Take the name of the servicing dealer (if its not the dealer you're buying from) and contact their service department to see if they can verify the service history.
See if you can find the thread about water pumps - there might be some useful information on that.
Hope some of this helps.