Daniel is it worth checking to make sure the solenoid is adjusted properly so that it will pull in strongly.

I have just pulled apart and cleaned my player unit( using your guide ta very much ) on my Card Whiz and I found even though all the parts were moving freely I had adjusted the solenoid just out of range of being able to pull the plunger in and if I went too far the other way then the arm connected to the plunger was just touching the solenoid housing not allowing it to pull in and therefore move the stepper around.
I moved it somewhere in the middle and it was fine.

Might be worth a check.