Should I buy

A clue as to how well the van has been maintained may be in the age of its tyres.  No tyre should be older than 7 years.  If any are, maintenance may not have been a high priority and they will need to be replaced.  You should also check for tyre cracking as this van must have spent a great deal of time stationary.  A check of the battery voltages could be revealing.  If either is significantly below 12.7V it shows it has not been maintained in a fully charged state which is life shortening and indicative that the battery may need replacing.  Try using the wiper blades.  If they are perished or worn they will leave streaks on the windscreen which is also indicative of poor maintenance.  Normally when oil or a filter is changed a label shows the date it was done.  Look out for this including the hydraulic oil.  If it has gas bottles their rubber pipes need periodic replacement.  As the van has clearly had long periods out of use, it would be worth checking the cab aircon still works.  If you buy the van without a proper record of its maintenance, the first thing you will need to do is pay for a full vehicle and habitation service.