I am not sure what you replaced as the fuel pressure regulator is part of the fuel distributer on the 380SL.
I doubt that fuel pressure alone could cause that much fuel. I suspect a stuck piston in the fuel distributor. There are a number of ways to test this. The easiest is to pressurize the system by one person turning the key off and on while you feel the airflow plate. When pressurized the plate should have instant resistance and smooth operation as one pushes down. With pressure the the injectors can be heard "singing" as the plate is pushed down. They should not sing with the plate at the rest position. This also can be determined by loosening one injector line at the distributor. NO FUEL should come from the fuel distributor with system prssurized and the airflow plate at rest. If the injectors are screeming when the system is pressurized and the plate moves freely to a point then the piston is stuck up into the distributor.
Bosch Master, ASE Master, L1
33 years MB technician