Brake cylinder at the rear? I wonder how that affects the behaviour left to right [or vice versa?] No noticeable clunk.
The single rear disk is on one side of the rear wheel,(not sure which as I don't have a M3W) so I suppose it it sticks on when applied so you could have more braking power on one side that the other, thus pulling the car. But I'd be surprised if it is that noticeable.
But if this pulling occurs on cars that have leaked oil I'd try changing the pads. Oil on pads can't be easily removed by cleaning.
