I just read through all of the TSB's for your car and the closest I could come to your hot starting problem was to replace the OVP, is that what you are referring to when you state the dealer replaced an upper voltage control unit?
How does it run after you finally get it started after it's hot? If it runs poorly i.e. stumbles, idles rough, misses while accelerating, etc. etc. than it could be a number of things.....I just resolved a bunch of running problems on my 95 E320 by just changing the spark plugs, they only had 21k miles on them but replacing them cleared up everything. I didn't have any codes with the bad plugs either......One of the TSB's suggests a faulty fuel pressure regulator too.