Gearbox noise

I changed the release bearing and the problems where gone…

but just when we came back from a 450Km trip the noise was there again.

The first time the noise was there after about 500km’s now it was back after another 450km’s so I guessed something was pressing against the release bearing all the time.

   The only thing that I did not change was the slave cylinder although that I didn’t had the impression there was something wrong with it I took it off and took it apart; on the inside there was a large surface that was corroded this prevented the piston to go back far enough when the clutch pedal was released.
This could be the reason for the clutch being slightly burned and the burned release bearing...