2 possibilities.
Be sure you do a very good clean out of the slot it fits in, I used a toothpick and a dentist pick, amazing how much crap I got out of there!
Also mine seemed to keep binding as I slid it into place.
I ended up putting a little more bend in the spring.
About 1/2 inch from the end that slides in, there should be about a 15 or 20 degree bend, just bend it a few more degrees, it helped keep mind from binding as I inserted it.
Hope this helps