Exactly, when the tumbler hits 9, the little pin engages to the previous wheel in line to spin it to the next count up, causing increased load. Turning it with the drill probably either overpowered it, or created a different loading on the gears/shaft.

I had success on mine without loctite, I used a pin punch, and struck it 2 or 3 times in the same spot to make a good impression. As the punch makes a hole, it also creates a ridged crown of metal around it, which acts to grab the gear. Has worked well for me now for a year.
I could see how temp would affect them, as the plastic gear heats and expands, it would be more prone to slip on that smooth factory shaft. (plastic expands faster/greater than steel)

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Chris
64 190D R.I.P.
80 240D W/617 engine -for sale
82 240D -for sale