father bob (Padre?),
had a 1993 300E 2.8 with a very very similar issue. Turned out to be a common problem component according to the dealer. A bad overvoltage protection relay starting to go bad, showing up as intermittent starting problems when engine hot. On a cool morning, no problem starting. Hot engine in the afternoon, rough start or no start at all, just cranking. Again, intermittent. After a new OVP relay, all was well.