I never knew the HPI or Traxxas 2 speed clutches would work.. I'd definitely go with one of those, if your clutch is already giving you problems..
But on a side note, if the setscrew to hold it on the shaft was missing, it wasnt stuck in 2nd gear.. You can also manually spin the 2nd spur and it should rotate freely.. If it forces the driveshafts to turn, its stuck in 2nd..  Also, the piece you found from the brake, is probably the little "button" that goes in the hole of the tranny, right below where the brake rod goes in. When the rod pivots it pushes that button out against the "shoes" and makes the brake shoes pinch the disk..