I had a thread on this somewhere...
You MUST measure the hub flange runout especially on older/used cars.
I was surprised how much mine had, so I replaced both front hubs.
Braking issue resolved permanently.
I had the on-car brake-lathe work, two disc sets from different manufacturers, always trouble shorlty after.
And the EBC discs were really crap - runout from the box exceeded BMWs oem specs, poor QC.
The big brakes on the 335 are especially problematic due to the large diameter - they need to be spot on.