Signcutter-we have always considered using the "twist grip" only in training and emergency. There has been a few ASB's on the solenoied and the use of the twist grip so I see it as a emergency function and not standard procedure as per the Arriel 2B1 but that is my interpretation.
Regarding the problem. If the co-plt twist grip operates correctly and extinghuishes the "GOV and Twist grip" lights then you need to replace the torque tube running between the pilot and coplt twist grip. This is quite a big job due to the amount of disassemble required as the torque tube runs internally inside the collective control tube.
Shout if I can help further or if you have more info