The semi-clear flexible tube that guides the PLA filament in my Replicator 2 started popping out of the clips on the back; the tube had many indentations from the two clips on the back of the Makerbot. On rare occassions, the tube would pop out and cause a failed print when the PLA filament got twisted and jammed. This simple part slides down from the top and holds the tube snuggly with a lot more surface area. The lower part of the hole where the tube fits is smaller in diameter so the tube won't push all the way through. After many hours of printing, it works great!
3 layer, 10% fill does the trick. No raft or supports required.