I am not a forklift tech, but I have three of these that I service myself regularly. I have learned a lot from these forums and I have a set of factory manuals. That said, I agree that the diagnosis on these can be tricky. I have had factory trained and experienced Caterpillar technicians look at my forklifts for electrical problems and be wrong, at my expense. Following a common sense approach to these is the smart thing. Also, verify everything. I have had joystick trouble as well. The joystick as a whole is a mechanical mechanism that as you stated can wear out, but typically all that goes wrong with these is usually the Potentiometer. If your trouble is sluggish control or erratic behavior, I would do the relearn procedure mentioned first. It is not as difficult as it may seem. If the symptom persist's and the mechanical components are not worn out, I would replace the Potentiometer and repeat the relearn. On the shutting down, if you can tap the board and make it shut down, disconnect the battery, take the connections loose on the board one at a time, inspect and clean them. if you see any corrosion or damage replace the damaged component. These are sensitive to voltage variations. They may be very simple, but they are logic circuits that function on low voltage signals. A.5 volt variation from bad or corroded or even loose connections can easily confuse the system and cause it to shut down. These circuits are very expensive and I would not replace them without some guarantee that the component has failed. There are some on board diagnostics available for much of these that will help you diagnose a bad board. A board sensitive to impact or vibration suggests that a connection is the likely culprit. As previously suggestted, a bad cable is more likely than a board and if a board has failed, there is likely a reason such as a weak or bad battery or cable. I tend to analyze the problem logically and plan a diagnostic process from that. Not always successful, but more often than not I find a simple solution I might have missed if I had jumped to the quick fix part replacement. In the automotive diagnostic world the rule of thumb is that the basic or simple problem is the likeliest, so stick to the basics and look more complicated only when all else fails. Obviously the technician that has seen these problems before has the best idea where to look. I have not had the shut down problem, but the joystick troubles I have repaired every time with a relearn or Potentiometer replacement. Incidentally, all these parts are readilly available from most any Caterpillar forklift dealer and there are many forklift parts suppliers that offer genuine Caterpillar parts. My dealer is as reasonable as the aftermarket parts, so I stick to the genuine Caterpillar parts with great success.