Likewise, this has just happened with my car. I thought about staking it, but in the end drilled a 2mm hole through the nose of the Al casting that holds the collar in place and through one side of the collar. Then inserted a 2mm pin with a length that just reached the other side of the collar and was flush with the casting on the outside. It was a lightly snug fit but cannot come out anyway once the filter is in place. I was surprised there wasn't any mechanism to prevent this from happening; circlip or something in the original design. In my particular case, the car is stored in an unheated garage over winter (which can get pretty cold) and have a feeling that the collar may get stiff and shrink more than the Al at cold allowing the slight pressure (and gravity) to allow it to slip. Now back in place at pressure reset to 2psi and car running OK again.