Noticed the eccentric gear before but now, started building the extruder, this looks unintentional :-)
Not found any one with similar issues in the RR blogs nor useful Google results.
This definitely won't drive the plasticfeed :-(
Sent BfB a mail and in the mean time, see how this part might be cut at the FabLab.
The extruder. The heater nozzle is to be built next.
The man holding the extruder, or that's how you feel after a good day's RR work :-)