Posting this warning for those with small children:
Last night my six year old managed to get his finger stuck in or near the rear differential of my 41999 - he is really fascinated by gears and wanted to see or make them spin. At the same time, he disconnected the corresponding L-motor from the IR receiver and attached it to the winch's power connector, and of course the battery was on, spinning the gears, wheels, etc.. After about five agonizing minutes, I managed to free his finger, but not before much wailing and tears. He is fine now, and lesson learned about machines and proper lock-out / tag-out procedures, related to his level of course.
Please watch your smaller children when they are playing with PF equipped models! Certainly in my house he will need to be supervised, I am planning to get a simpler model he can build to help him learn about gears and rotating devices.