I've had issues in the past with my drive gear "eating" my filament. It seemed that the filament quit extruding for one reason or another and the drive gear would slowly eat away at the side of the filament.
I eventually assumed it was the plastic filament guides causing unnecessary tension that the drive gear couldn't compete with, ultimately keeping the filament from moving forward. Thusly, allowing the drive gear to continue "trying".
My solution was to hang my spools above the machine to avoid using the filament guides feeding from the back of the machine up through the top.
Can the plastic filament guides really cause that much drag? What other variables can I expect to look out for?
Machine: MakerBot Replicator Dual (1st Generation)