That's pretty low miles for a csc failure, although it seems to happen even on newer cars, so who knows.
The only relationship between the brake fluid and clutch is that it's the same type of hydraulic fluid used in both systems. Other than that, they are independent systems in this driveline. Some mfg's do use the brake reservoir as a source of fluid for the clutch. This isn't one of them.
The clutch one is the smaller of the 2 in the pic above.
If it's the same bulletin i've read before, it involves changing out the fluid to that of the gtr brake fluid (higher wet/dry boiling points). I guess that's a starting point rather than dropping the trans to inspect for a failed csc.
I'm guessing you never flushed/bled the clutch fluid? It is possible there was moisture/an air bubble.
Let us know what they find.