So last weekend, I replaced the rollers on my Barley Crusher. Right away, I could feel that the knurling on the new rollers was much sharper than on the old ones.
This morning I milled some grains for an APA and it was crazy how much harder it was to crank the mill (I usually mill by hand) though I left the gap at the factory spacing.
Anyway, it totally fixed the problem of having the non driven roller stop turning. I wasn't sure before what was causing the issue, but it definitely appears to be a wearing down of the knurling over time. I think I bought the mill originally in the second half of 2007.