The opening in the trunion is made a fraction to big on some of the Airpower retracts. Seen it many times.
A solution except for returning them for new ones, is to use alu tape one or two rounds around the strut. Then remove the screw in the trunion and force it a bit more open with a flat screw driver so you can insert the strut without damaging the tape.
Worked well for me.