I don't think it's a "slack" that you are adjusting, because I did this on my Legacy's sunroof, and the "nut" you are talking about is really a preload to a friction plate wich is adjusted to just barely slip when the sunroof comes to fully closed or open, so that the motor would not stall and burn.
But maybe it's diffrent on the SVX, I'm not sure.
/Sonny
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Internal name: "
SuperSonic"
-92 ebony black with 170k KM
*** -Stress is when you wake up screaming & you realize you haven't fallen asleep yet. ***