I have a Kubota diesel compact tractor that I use Shell Rotella T6 full synthetic oil for. The last time I changed the oil I bought extra so I have an unopened 5 qt jug and another 5 qt jug that I used about half the oil out of. I know the unopened jug is still good but I'm not sure about the one that was opened. It's been in a cabinet in my shop since last fall. I know brake fluid that has been opened and left is no good as it absorbs moisture. Is unused oil stored in a container with the cap on still good? I know it may sound like a stupid question but I usually buy oil for my vehicles in 1qt bottles and use them as needed. Thanks