not starting when hot C250diesel 1994
 

When the engine is swicthed off after a journey time of over half our hour and left for a period of say ten minutes. The key will not turn in the ignition to start engine. The only way to start it is by shorting the starter. Then it starts first time. The local dealer has fitted new earth lead to starter, new key barrell and bypassed inhibitor on auto gearbox. Also fited new gate to gearbox inside car. all to know avail. Can you help please. As they have given up.