1. Breaker: Easy to check, probably not the cause, switch it with another breaker of the same amperage.
2. Short: Probably not the cause either since it only does it occasionally, unless, when the water reaches a certain level it bridges the gap and causes the short.
3. Overamp: Most likely cause- two possibilities:
A. Pump is partially jammed or binding from old age. Since the pump is not turning freely it is putting a strain on the motor causing it to overwork and heat up. When this happens the motor begins to exceed the amperage rating causing the breaker to trip.
B. Motor itself. As motors age the internal parts break down causing problems. Either the windings become shorted, the bearings begin to seize (similar to the pump problem), etc. For whatever reason the motor will itself overamp and trip the breaker.
The overamping can be verified with an amprobe without going into the well.
Notice the diagramming, paid attention in school. I am not certain what your control box does, but I really cannot see it or the pressure switch causing a tripping problem unless it shorts out from the water. But all of these are usually under water constantly unless yours is a remote setup.
If I missed anything?????