It will never "clear up", but may not get much worse (most likely will, though). It's not moisture, but a loss of liquid crystal, as I said in my last post. Nothing will bring it back
Temperature affects the size of the defect due to the expansion and contraction of the materials and crystal that come with temperature changes (the affected area will appear smaller in warmer temps, larger in cold).
Sadly, replacement gauge cluster LCDs cannot be purchased.