The clutch on my A4 also slipped at some point, but not always, only sporadically. And the brake grinded again and again, even though brake calipers were new. That's when I first suspected a connection.
When looking at the clutch master cylinder (on the pedal), moisture in the form of brake fluid was discovered. So it was obvious that the cause should be sought here and not on the clutch itself. Both systems (brake and clutch) are actuated via brake fluid.
I then had the master brake cylinder and the brake servo replaced, because you couldn't say exactly what it was now and I wanted rest and no further intervention with loss of time.
Since changing the two components, the clutch has not slipped for several 10TKM and the brake no longer applies by itself.
Maybe you can have a go there.