The Brownian Gate capytalk expression seems to have the form:
1 brownianGate: 1 s deviation: !Deviation s minDur: !MinDur s maxDur: !MaxDur s dutyCycle: !DutyCycle
It's "brownianGate" instead of "brownianGateStart"
The Brownian Trigger expression on the other had does end in "Start":
1 brownianTriggerStart: 0.1 s deviation: !Deviation minDur: !MinDur maxDur: !MaxDur
Here's a sound with both expressions in it.