The stock CSC's are pretty much plastic, and known to failure but once that happens you're usually getting a towed home, at least that's all I've read. You can also get under your car open the inspection plate on the trans, and see if you have any oil in there from the CSC, and that would be a good indication of CSC starting to fail. This is just stuff I've read, so take it second hand.
What the problem might be, and this is what I ran into. I boiled my clutch fluid, and it did the same thing your talking about. I think it's cause the clutch line runs pretty close to the cat on the driver side. I had the clutch system flushed out really well, and had zero issues after that for the next month, then I swapped everything out cause I had jumped the gun thinking my CSC was toast, and ordered everything under the sun for the trans from
ZSpeed Performance Oh yeah, and Nissan doesn't cover the CSC in their drivetrain warranty.