Overfilling any auto box can cause foaming of the fluid which can cause fluid to escape via breather. The gears act as a whisk. The hydraulics like brakes do not work too well on aireated fluid. I've only seen blown seals when the breather is blocked. I think it breathes from the top of the dipstick tube.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix cars.