On your current setup, when you said your armrests were slipping or had slipped, was that the whole extension moving or the armrest moving on the extension?
I had the same problem with the Vukas. The only way I could prevent slips was by using lots of Tacx assembly paste and tightening beyond the recommended torque.
Do you have a picture?
On your current setup, when you said your armrests were slipping or had slipped, was that the whole extension moving or the armrest moving on the extension?