Master Cylinder, Booster, or both???

[JayG]

My brake pedal feels a bit soft. The brakes work well, just not a hard pedal
It manifests most when I am at the track. Its not fade, or brake lines , or air in the lines.

I have done a full flush and bled the lines a few times. Fluid is fresh Motul 600 and new pads. I don't have any fluid loss either

Sometimes the pedal is rock hard for a couple of time on the pedal, but most of the time it just feel soft. It doesn't bottom out and if I pump it it gets a little harder, but still not what it used to feel like, rock hard.

Like I said, the brakes work well, just doesn't feel right and it causes me to brake much earlier than I would normally at the track.

I'm thinking it may be the booster or the master cylinder or both

Thoughts??