If flashing keeps failing with DreamUp, you must consider a broken I2C chain. This is almost unreparable unless you can actually see something wrong on the PCB. Due to it's age you will have trouble to have it repaired. Mainboards are available at idiotic prices.
Best option is to get a second hand DM8000 if you want to stay with the DM8000 or simply get a new receiver..
The I2C bus is connected to every section of the hardware. Since you experienced problems before it may be as simple as a blown resistor(pack) or capacitor..