I had that problem, I flushed out the grease with wd-40 or smiple green. Than used Phil Woods Oil
or a similar oil. I haven't had any problems down to -20, even with bike sitting outside all day. I re-
apply the oil about once a month, more if the weather is really damp.
There is a lot of other reading, by doing a search on it. It's a question that comes up every cold
weather season.
That should help with your problem, now go out and enjoy your communtes