Try this for a difficult clutch?

ZoomZ

I also had black fluid after about 10-12K KM's. I flushed completely and used Motul RBF600. Made a huge difference.

I had a whining CSC but not failing. It never leaked. However, after the CSC was replaced under warranty, it was again appreciably better feel.

Unfortunately, I forgot to give Dealer some extra RBF600, so they used their DOT4. The book calls for the GTR fluid (mine is NISMO) but I doubt they would do that. That's ok, I plan to flush in 10K km or less depending on fluid condition.

I use Motul 5.1 in all my other Nissan's. Murano and Xterra. Excellent brake feel.