I'm a pool and spa guy and these pumps are very similar in design to what I work on daily. Heck some of them are made by the same manufacturers. In my experience when a pump shuts down but struggles to start spinning again it's usually due to a burnt armature. Basically means your bearings are bad. The pump uses magnetic polarity to start and keep spinning and if you have a burnt armature what happens is depending on where the shaft lands when it stops spinning it may not be able to start spinning again( will over heat and trip the capacitor) this is why you are able to still get it going by spinning the shaft. How old is the pump? If this is the case which it sounds like it is, really the only thing you can do is replace the motor.