Several have posted about there collar not holding the shaft in place.. One of my old Terrovas had that issue.
Here is what I did to mine. One picture is of my new Ultrex which is not slipping YET. Notice how the collar is totally compressed where the bolt is, yet has a noticeable gap next to the shaft.
The second picture is the modified collar from my old Terrova.. First I filed the inside of the ears a little then made an aluminum piece to use as a stiffener. Worked for me !!