Make sure its the tank....you may find if the levels are too high in the tank, the fluid seeps through the lid and ends up on the tank....as me how I know. The correct level in the overflow is down lower than you think. Look in the tank for the X piece sticking up. My guess is the expansion at higher elevations is more, therefore, you may get some coming out. Just an FYI, also, if it makes you feel better replace it, but if you have coolant again, check the levels.
Ed