Rear view mirror

My mirror was some sort of automatic high speed cut-off. Everytime I reached 120 kph it flipped against the vent window due to the wind load. I tried several times to tighten the nut to achieve higher clamp forces, but the material is so weak, I stripped the thread!
Luckily, we have a huge "helicoil" repair set in our company, which I borrowed today.
This is the problem: 

 No clamping force on the spring, as the thread in the lower nut was stripped.

Here is a detail shot of the stripped thread. When I drilled the new hole for the thread the material appears to me like aluminium, super soft!

The helicoil insert is clearly visible, after re-assembly it appears a lot stronger. Tomorrow I will give the Volksback a "high speed test" to check if the mirror stays as adjusted...