Could be the starter, or battery, or ignition switch, or wiring, or...? I can't think of any reason moving the car would spring the starter to life, other than it gives a bit more time for before giving it another attempt?
I don't have any experience working on DOHC starters, but I can imagine they are very similar to the SOHC starters. My experience with the SOHC starters is that the solenoid fails because the copper plate inside the solenoid that, transfers voltage from the battery to the starter motor, arcs which erordes material and deposits crud. The combination of built up crud, and lack of contact caused by the erosion, prevents the starter motor from getting sufficient current - thus preventing the starter from engaging. When that happens, you should hear a click at the starter solenoid, but nothing else. If you don't even hear a click, the problem may lie somewhere else.
BTW - that copper bar that transfers power from the battery cable to the starter motor will erode and accumulate crud faster if low voltage is transferred. In other words if you have other problems like a battery in poor condition, poor electrical connections, weak solenoid, etc. the problem is accelerated. Other than ensuring all of the connections are clean and tight, a starter solenoid - for the starter solenoid - is a good idea. (I'm not sure if the Scorpion has one from the factory?) I like a starter solenoid - for the starter solenoid - because it helps keep the starter solenoid in good condition, but it also takes some load off of the ignition switch. Well, that and your starter might perform better!
