Could this perhaps be down to:
- Wear. Glazed pads, permanent deformation due to overloading of the spring somewhere in the past;
- Wrong assembly. Wrong position/seating of the parts and/or non-original parts that are not compatible with one another (plausible with a second hand car);
- A production flaw. I didn't have it with Asso but another brand where the hole that seats the slipper plate onto the topshaft was. If the spring or the threaded portion of the topshaft is too short you might also not be able to build up much pressure before 'full lock';
Depending on how much you need your slipper, the cheapest solution would be to glue the thing shut... Not elegant, but if you create a strong bond, quite effective...
