92 500SL, bad fuel pump?
 

Turns and turns when cold, won't crank, when warmed up will crank right up. If cold and I hold the key in the accessory position for a few seconds, it will crank easier, however I can hear the pump buzzing and then stopping, over and over. It doesn't buzz and stop like it normally would

If you remove the MAS relay & bridge pins #1 to #2 the fuel pump should stay running to see if that is the problem.