During the hot weather my starter would hesitate to roll the motor over when it was warmed up and when you did multiple stops, like running errands. It simply went away with the cooler weather! I understand there is a current draw test where someone measures the induced voltage in the wire while the motor rolls over. I think some parts sellers will test it when it is out of the car. There are lots of connection points in the starter system so you could clean and tighten them and put the dielectic grease on the connection points, and that is a free fix if it works. I have heard of "bad spots" on the armature on the starter and if the starter brushes stops on one of them, it is hard to bump it off that spot, but that is a long shot. I never liked the starter being right under the oil filter which is mounted on an angle, so oil always runs out when removing the old filter. Have you had an oil change lately?
