Please Help ! Warm start problem

Hi,
I would greatly appreciate any help with a what appears to be a warm start problem:
My 94 E420 (62K-starmarked) is displaying the following (mis)behaviour:

After driving it for 30mins plus at speed of 65mph+(highway) and shutting the car off for a few minutes, it refuses to start again (engine temp>85F). It cranks fine and all of the instrument lights illuminate (suggest electrical system integrity) but it will not start. At 40F, it will start if you press the accelerator but shuts off if you discontinue fuel supply. Leave the car overnight and it starts fine.
Also, if you drive it around town, it restarts fine. There is something about 30min+ highway driving that it does not like (heat generation is larger, causing component expansion/ failure and fuel system malfunction??).
My dealer also kept it for a weekend, putting 300 miles on it and failed to replicate the problem.
Any ideas - it seems to have my dealer perplexed.
thanks
farrukh

[Benzmac]

Two things. The fuel injectors have been known to fail on this model. You have to replace them if failed. The other thing I have seen is the distributor caps will corrode badly. Take them off and you will see it quickly if they are bad. They will have a green inner tint if faulty.

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Benzmac:
1981 280GE SWB
1987 16V
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