>I did need a swipe with a sensor brush on the mirror to rid it of
You should never use a sensor brush on the mirror or camera chamber. You might pickup a small amount of lubricant that you cannot see and transfer it to the sensor. This might make a dust particle stick to the sensor. You can use a lens brush on the mirror, and then blow out the camera chamber with a rocker blower.
Sensor brushes should never touch anything but the sensor. VivibleDust sells a sensor brush cleaning solution.