Cat C12 bad oil pressure sensor or bad gauge

Hi there,
I have a 2004 Sterling with a C12 and my oil pressure gauge seems to have a mind on it's own. It works fine most of the time but when it get around 45 or below at night it wants to play "dead" in the morning. While all the other gauges peg out and back after startup the oil gauge does not move. The engine runs fine and there are no warnings. After some time when everything warms up the gauge will get unfrozen and will indicate some oil pressure. If I stop the engine and restart it the gauge will work normal. Also while driving yesterday the gauge moved to twice the normal reading with no warnings. After a restart it was reading normal. There is always plenty of oil and I only use Cat filters.
My question is, bad gauge or bad sensor ? If it's a bad sensor I would think the ECM would throw a code or try to shut me down ? Is the ECM getting the pressure info from the same sensor ?
The gauge is part of the cluster and can not be replaced individually so any help is appreciated before I start throwing parts at it.