Mazda's a small company that likes to do everything in-house, so I get it. Pretty sure Getrag makes an AWD manual transmission that can take the power of the 2.5t, but Mazda's never going to buy a transmission from a third-party supplier.
I've also had the buildup issue on my Stinger, though it's pretty mild, so I'm not too worried about it. If I have it long enough to put new front pads on it, I'll be doing the Euro-spec pads that everyone claims fixes the issue.