Just to add to the thread: I've been helping a friend with his WGen9500df.
His first and most serious problem was that the compression release on the camshaft failed, with some corresponding internal destruction. The automatic start system didn't recognize that the starter motor was under heavy load which burnt the windings. Finally the recoil starter rope broke, delaying figuring out the underlying problem.
A few months after that problem, the remote and panel pushbutton automatic start system failed. The problem was identical to the other postings: water intrusion into the switch caused the contacts to fail. He usually kept the generator under cover, but needed to open it for running. There is a constant +12V in the switch, so even a drop of water wicked into the switch will result in rapid corrosion and little opportunity to dry out.
The first time I swapped contact sides on the DPDT switch (the engine kill side uses only the 'off' contacts, and the radio/start side uses only the 'on' contacts of the other throw) but the problem has recurred. Eventually I'll find a better waterproofed switch, or perhaps buy the upgraded switch if it is in stock when the problem happens again.
Note that once you know this is a problem, it's easy to confirm by checking the voltage on the 7 pin ATS (Automatic Transfer Switch) connector.