Hello, I recently put in a second HDD in my Macbook Pro Mid 2012. Unit works fine. Intermittently the unit will not boot and will not find the OS HDD original one. I have to sometimes hold the option key when powering on unit to select the HDD with OS installed. although sometimes will not work either. After a few power downs and power up it will find the OS. Can someone please assist if they have come across this issue or a fix.