Some Home Brew Tailshaft Balancing

I finally devoted some time this weekend to attempting to improve the vibration issue with the Vogue's tailshaft.
I had bought a 3 axis accelerometer from eBay a few weeks ago and on Saturday I added some connectors and wires so I could select any of the 3 axis to test. I choose the 'Z' axis output set to high-sensitivity, and added some orange bluetack (yes, really)  to the bottom of the PCB to hold it on the motor frame.
The bluetack colour got washed out on this picture as and appears white.

Up the Vogue went onto axle stands with the rear wheels removed for safety.
I cleaned some road dirt off the motor frame and stuck the accelerometer on.

Then  I limited the motor speed to 3500 RPM which is 87 km/hr so that the tests would be repeatable - all I have to do is floor the accelerator.

I dug out my 38 year old 12V power supply and the CRO.
 
First trace. There was a lot of motor controller PWM noise but the vibration waveform was clear. I later added a 500Hz single pole RC filter which cleaned up the motor PWM noise - sorry not shown here. So the start point was 100mV P-P.

I wrapped some masking tape around the motor end of the tailshaft and marked it in four sections. Then I applied a stainless steel hose clamp and tried all four sections to see if there was a change.
Results:
1  200mV
2 30mV
3 160mV
4 175mV

Then I tried in between but I couldn't do better than the result in number 2.
I increased my test speed to 4100 RPM (102 km/hr) and tried all again. The vibration increased to 50mV with the clamp in the best spot - about 1.8.

Picture here is with the clamp at about position 2.5.

I tried adding a small washer but there was a slightly worse result.
I tried cutting off 5mm of the protruding part of the clamp, but if anything, the result was slightly worse. It was hard to tell.

So I left it at position 2.

Conclusion: It is possible to significantly improve the vibration problem.

Curiously, position 2 is where all the balance weights are currently welded.

Not sure what to do next - thinking...
I'll drive it tomorrow.