I am no expert, but it may depend on how your system is made. In my red 5S all I know is that a couple of well known vendors said to never use silicone in the system (I believe it is some C5 brake system, but will need to look after I sober up). Maybe the issue is changing over, to be sure all the other fluid is flushed out. Or maybe due to having rubber or silicone implant components makes a difference?