If it won't crank the first thing I do is jiggle the shifter a little in park, then try it in neutral. If the neutral safety witch is acting up, this may help.
Pretty common for the brushes inside the starter to wear down. You can often get a start or two by hitting the side of the starter with a hammer (moderately), it seats the brushes down a little deeper.
Also not uncommon for the oil filter adapter "O" rings to seep and cover the starter in oil, someway the oil finds it's way inside the starter and coats the brushes, which can also cause iffy starter function.