Trying to crank a M120 on a crappy shim job is prolly the problem, its only being made worse by thermal expansion caused by the cold weather. Also, a 8.4v 1100mah battery is below what I could suggest for trying to crank a M120 JG gearbox... if it's one of those shuang buang deals then that is most certainly your problem.
Condensation could also be a problem, a cold gearbox being heated by friction will tend to cause droplets to form, these could be freezing and causing problems within the gearbox itself, again only made worse by JG's horrible shim jobs and the INSANE amount of lube they put in the mech boxes.
Also, the freezing temp of the grease could be well above 0c depending on what its made up of, keep in mind that propanes boiling point is like -15c, everything freezes and boils at a different temperature, general use of the term "freezing point" is used only for water.
In short, have a gun doc reshim/relube the gearbox and tune the motor adjustment height, upgrade to a 9.6v 1200mah battery. Hope this helps, be safe
