Boiling is a common practice used to increase the strength and reduce the brittleness of plastic parts. It is analogous to the practice of "heat treating" metals as done with parts for aircraft engines. The concept is to get it up to a temperature where the molecules can move around more freely, then slowly cool the parts. When this is done, as the molecules slowly slow down, they form a more crystal-like structure, giving the substance greater strength. Again, the slow-cooling of the parts is critical to this process.
It is recommended to boil the E018 (tail shaft input gear), the E028 (Tail Gears) and the tail assembly holder (E025). Boil these at a simmer for about 30-40 minutes, with screws inserted to keep the holes from closing or warping.
The Main Gear E002 cannot be treated in this fashion, or it may be subject to warping. Though we are awaiting more feedback as to people's success with heat treating the main gear, several people have reported placing the Main Gear in tap-hot water, and letting it sit and cool overnight with no warpage.