Hi, I had the same problem with my 96' T4 Transporter (350.000Km's) after months of frustration I located the the offending part, the igniton switch. It is removable, held in position with a small screw under the steering column, inside the switch well. As the screw is impossible to refit, I secured the repaired switch with a cable tie. No more starting problems for the last 3 years. A friend has the same car, had a similar problem caused by a cracked solder joints on the ECU (Computer), this was an easy fix by a radio technician.
Henry Banninger
October 2007