You'll need to add:
Code
<register event="gainbuff_Copy*">sc set RancorCollar;</register>
Might also work if you have a set specific to rancor collar in the SC, this is what I use for berserker's torque:
Code
<autoexec>
<register event="gainbuff_Sleep*|losebuff_Sleep*|gainbuff_Aftermath*|losebuff_Aftermath*|gainbuff_Haste|losebuff_Haste|gainbuff_Last*|losebuff_Last*|gainbuff_Embrava|losebuff_Embrava|gainbuff_March|losebuff_March|gainbuff_Voidwatcher|losebuff_Voidwatcher">Update</register>
<register event="gainbuff_Sleep*">sc set BerserkerTorque;</register>
<register event="hpp_*|mpp_*">Update</register>
<register event="tp_0">Update</register>
</autoexec>
Hopefully some of that is applicable to your situation.