The replicator 2x is an impressive beast and handles ABS quite well (after you plug all the air leaks at least). However I certainly do have issues printing with PLA and I have recently come into contact with other replicator owners who report similar issues. So in the interest of making the internet a more informative place I present you with "PuZZleDucKs PLA Printing Tips".
Airflow:
It seems that PLA and ABS disagree on what is a good print chamber. While ABS likes a closed chamber PLA likes the open air, so remove the lid and open the front door. This alone made PLA easier to print.
Now take that a bit further and add "active cooling". For me this is a cheap $5 fan placed on the top-back-left corner of the replicator pointing towards the build platform. There are a host of these available on thingverse (like this and that), but they all seemed way too over engineered and fiddly by doing things like mounting the fan on the print head. Way too hard when the cheap little fan does an excellent job.
Extruder:
It seems to be my impression that PLA is a bit softer than ABS and so it helps to have an extruder with a filament guide tube. Why not print every one you can find and try them all. There must be more by now, let me know if you find any other good upgrades.
A slight caveat to this is that I did my upgrade with a separately sourced spring(the C-624). Recently I had one of the makerbot upgrade kits delivered and the spring seems to be very weak compared to the general propose springs I already had. So if nothing else here has helped you may want to try alternative springs.
Voodoo:
Just kidding, but this one is not far off. While the PLA is loading add a drop or two (not much) of extra virgin olive oil to the tip of your index finger and gently rub the filament with the oil just as it gets pulled into extruder. I don't know why or how it works, but seems to be essential for my machine to print certain reels of PLA. The good doctor has some ideas about why this may work (and he's also my source for this here tip).
Hope that helps you all out and let me know if I've missed any tips or tricks for PLA.
