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2006 Chevrolet Colorado - Leaking

Why is there air coming out of the oil filler cap and dipstick ,and oil seaping out of valve cover where cover meets the cylinder head ?

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That’s not air…

There is always some pressure in the crankcase caused by combustion gasses getting past the piston rings. As the piston rings wear, more gasses get past and the crankcase pressure goes up. That’s what you are likely feeling as the oil cap. As for the valve cover leaks - the truck is 12 years old (and has ??? miles - you didn’t say) and likely needs a new valve cover gasket.