I just spent an hour cleaning out the extruder -- I'm always nervous about this kind of thing, as I'm more persistent than experienced when it comes to my electronics' innards. I ended up cleaning out the gear teeth with a Xacto knife, with just a bit of trouble getting the spring lever arm back on. (Not to mention that when I took that arm off, a small brass collar fell out. I didn't actually know where that went, but I put it back as an interior sleeve around the screw that holds the arm on. Seemed to fit, and seems to be working...)

Anyway, my filament is feeding again, and I think from now I'm going to try the snip and load process that people mentioned earlier here, rather than the unload and re-load.