I am having similiar issues with my 1991 300 sl . Morning starts are normal, after sitting for ten minutes to 1 hour the engine stumbles to life, after sitting outside in the hot sun ( 75-80 degrees ) this is my worst condition , it will sometimes require several attempts to get started,starts after short shut downs such as refueling are normal. Can flooding from leaking injectors be a problem after 8 or 9 hours if the vehicle is sitting in the hot sun??I was thinking about pulling spark plugs to see if they are fuel soaked to verify flooding ... any thoughts? Thanks dan