Paul,

I have a 98 ML320 with a similar problem. The car stalled on my wife during a hot day. No Check engine lights appeared. I replace the Crank Sensor first. The car ran great but once the temperature gauge read around 85C and it is stop normally and allow to set for about 10 to 20 minutes it cranks( motor turns over but want fire). Open the hood allow the engine to cool down to about 80C and it fires right up. When it is cold it fires up everytime.

Next I replace the fuel pump and filter. The same problem occurs. It ran great down the road but when it is stopped and heat soaked it will crank but want start. Does not give a check engine light at any time.
It will start somimetime if you stop it and right way after restart.
Once it is hot it want start. It appears to be sinsitive to the temperature of around 85C. Any ideas.

Regards,
Don Mel