During cold weather, the hoses and various plastic and metal components they connect to experience some severe temperature fluctuations. Because the rubber and plastic/metal expand and contract at different rates, the temperature fluctuations can create leaks. Try tightening all the hose clamps that you can find in the cooling system (particularly in the area where you found the fluid). Then top off the reservoir and keep an eye on it. If it's still leaking, you might need a new waterpump or you may have a crack in the system somewhere. Tightening the clamps won't cost you anything, so you might as well try that first . . . you may find evidence of the leak while you're doing it too.

Good Luck

Rich P.