If you buy the TM recoils from Echigoya in Japan you will save heaps of money even if you get shafted on shipping.
I'm not going to go on a rant about how they are not near 11.1v lipo ready even though they are advertised as that.
Instead look at this freshalicious casting on the gearbox. The uneven swirls show the low quality of the zinc alloy used,this is something you often see on ACMs not a high end gun like KWA.
Apparently,there are also a fair amount of failure reports on the 9mm bearings on post 2011 models,though I cannot personally confirm this.
This is a bit of an old video but shows some issues.
*youtube*
*pic*