Try this for a difficult clutch?
 

I've read over and over how the Z has a difficult clutch to modulate. My 2015 daily driver/auto X Z has been trouble free and easy to drive since day one. I have about 38,000 miles on the car, but recently I found myself stalling occasionally. Then it started to require more pressure to press the clutch to the floor. It was actually getting very noticeable.

I figured I was just experiencing the classic CSC failure but I haven't lost any fluid yet. The reservoir was full but very dark. Before ordering "the kit" I figured I would just change out the fluid.

I bleed half a bottle of cheap dot 4 through it then filled the system with some 5.1 I had. This absolutely fixed the crapy clutch feel and requires less force to actuate. Its like a new car again. I'm thinking the old fluid was just cooked.

My question is this. Is DOT 5.1 ok long term for the CSC? I know it has a thinner viscosity but it should resist higher temperatures right?

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.

I have been flushing mine every 20k miles with the same motul600 when DD, and every time before track day. I made a bet with my friend that i lost recently, cqc made it over 70k, in nyc Daily Driven traffic, also it is very important to not ride the clutch, it was not ment to be used like that, most cqc falures occur due to clutch riding, so try to avoid that, just clutch in/out.

This sounds like the early signs of CSC failure. Your Genuine Nissan CSC can catastrophically fail at any mileage not just from improper use of the clutch riding the clutch petal or dumping the clutch petal. I have had to replace the Genuine Nissan CSC three times before installing the Z Speed Performance CMAK. I highly recommend replacing your CSC with the Z Speed Performance CMAK kit before it’s too late and your Z ends up riding on a flat bed tow truck three times like my Z did I hope you have AAA. Bleeding and replacing the brake fluid is only a bandaid or temporary fix before your CSC eventually fails and leaves you stranded. If you decide to wait for the brake fluid to leak since the Genuine Nissan CSC is located inside the bell housing it will quickly saturate your clutch and ruin your clutch as well as cause your master cylinder to leak brake fluid and the brake fluid can actually leak in the foot well inside your Z ruining your interior of your Z. Clutch and flywheel set ups are expensive to replace on our Z’s. Our Z’s are also prone to master cylinder failure but CSC failure is very much so more common. I highly recommend bleeding and replacing your brake fluid with either Motul RBF600 or Redline brake fluid as soon as possible before your brake fluid boils. I bleed and replace my brake fluid every 10K-20K miles or before and after every track day/event.

So 5.1 is a no go?

You're good .... DOT 5.1 in the clutch is fine

Like the big guy said. You're good to go. Just don't use the 5.0 stuff.