you are right I had exactly the same problem.
Here is a brief overview how to flash the hephestos 2 with the original Marlin FW.
I downloaded the software from http://marlinfw.org.
This is the source code. The config files for some printers are in the sub-folder "examples".
Just copy the 3 files in the Marlin root directory.
I made these changes in the configuration.h file.
#define Z_PROBE_OFFSET_RANGE_MIN -4
You must install the Arduino IDE from https://www.arduino.cc on your PC.
Inside the App you must download the U8glib and update the libraries
Set the board to Mega2560 and the port to usb.
Connect your printer to the PC and click "upload". The Arduino IDE will compile and upload the firmware to the printer
How to setup the Z-Offset with the new firmware is explained in this little video.