I have a 1997 E300 diesel, 160K miles, which has developed an intermittent problem which unfortunately is occurring more often - three times this week. Sometimes I cannot start the car. The engine will turn over but will not start. At that time the glow plug light is out and stays out. I have had it towed to my mechanic twice and each time he checks the diagnostics and says it is a security (key) issue. He has suggested we lock and unlock the car a couple of times and it should start. We have also tried using different keys. That certainly did not work this morning. The alternative would be to completely change the locking system. I just feel this may be glow plug related. Any suggestions, please? Thank you.