Brother initially told customers that you can leave maintenance solution in the printheads. However, they quickly realized that the maintenance solution dries out quick which will then dry out the printheads. Once the printhead dries, there's not much you can do to save it.
My first year with Brother, I put in maintenance solution during winter season right after the holidays. I had the machine off for about 3 or 4 weeks and when I came back, the white heads were never the same again. Under warranty, Brother replaced 2 of my white heads. And shortly after that they told me not to do that again.
I think it's Brother's fault for informing customers that it's safe to leave maintenance solution for a long period of time of being turned off. However, this is not true and your white print head needs to be active. Once the white ink has gone thru the printhead, you can't turn "off" the white head.
However, this is a characteristics of every DTG printer, not just Brother. I now have the GTX and it does auto cycle and auto cleaning of the white head. The auto feature wastes some ink, but it's a whole lot less than GT-3's flushing and maintenance. But like the GT-3, the white heads, once the white inks are introduced, it can't be turned off.