Changing oil after car sitting

Bought a 1990 Chevy van last year and drove it most spring/summer as a 3rd vehicle, but it has been sitting since October.....I did a synthetic oil change on it in spring and it only has been driven about 600 miles.....should I change the oil due to sitting...I'm thinking yes

also, I noticed the overflow coolant reservior is almost empty ....could of sworn I topped it off when driving it....I though the system was sealed.....how could it be so low?

Thanks

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RIP Bucky - 7/25/1943 - 1/19/2013