When I bought Tigger, he had Koni Sport Shocks on both front corners, but only one rear corner, after contacting the first owner (I bought him from the second), it was apparent that there had been an issue after he sold it, and the second owner had ONE shock replaced with an OEM one.
I did a lot of digging, both here and on other forums and found that the Koni Rears sometimes have an issue with losing the clip ring that helps hold everything together. I sourced out a Spiral locking ring that had the same ID, OD and width as the original (I thought) as well as a new rear shock.

Last night was the truth test, the spiral locking ring worked until you put force on one side of the collar and tried to get the ring to engage solidly. I then went back to the original ring, and found that if, when you install the collar over it, if you engage one side and then push remaining bit of the ring in (I used a small flat blade screwdriver), the collar will snap over the ring and lock into place.
So I am now assuming that when people put these shocks on, due to the miserable pictographic instructions, they don't think to lock the ring under the collar, they are simply PLACING the collar down onto the ring, where it can be popped out of place under impact.
So I'm posting this to try to help others when installing the Koni Sport Shocks, BTW Tigger is an '05 MCS.