The cold weather thing is still the float switch in the m/c reservoir, getting hung up because of different rates of contraction in the hinge area of the float between plastic and metal. Brake lube the hinge, working it up and down while doing so. Ditto the rubber air over the fluid seal, which should only protrude to fluid level when installed. It's there to allow volume changes in the reservoir without exposing the fluid to humidity in the ambient air, since the fluid is hygroscopic (likes to suck up water, which will boil when it gets hot enough and you won't have didddly for brakes).