I had a similar issue on my DI LE and discovered it wasn't anything underneath. In my case the culprit was the plastic mold of the mechanic's body, which covers the diverter mech, was impeding the full motion of her arm. As I was looking underneath the playfield and checking out the components mentioned above, I noticed there was some slight tension in the rod as I moved it up and down. By accident, I grabbed the plastic mold of the mechanic's body and moved it slightly and suddenly everything freed up! The rod and diverter now moved freely with no issues. But the plastic body mold wouldn't stay in the place I needed it to keep the diverter arm free. So I removed the two-tiered plastics to her right and loosened the two Phillips screws near the bottom of the plastic body mold. Then I was able to slightly rotate her body counter-clockwide just a little bit in order to free up the mech. Once in the right place, I slightly tightened those same two screws, but not completely so that there would be a little wiggle room to keep the body mold in place. During each step of reassembly, I re-tested the diverter to make sure it still moved freely. I've since played several test games and it's been working great. I've only had my brand new DI LE a week and now I'm happy that it's working 100%! So if the rod, spring, and set screw underneath the mech isn't the culprit, try my suggestion and that might solve your issue.