Small Engines (Lawn Mowers, etc.): onan, hairline crack, random problems

Question
I have an 1991 Onan 4.5 generator and it runs great. Every once in a while it will quit. If I hold the start button it will run, sometimes will stay running when I release it, sometimes I have to hole it for 30 seconds to finally keep it running. It has remote start controls and I tried unplugging them and nothing changes. Very random problem, sometimes 5 times a day, sometimes none. Circuit panel?

Answer
There maybe a small, hairline crack in the circuit panel, a slightly defective solder joints or corrosion/defective switch.
Random problems are the worst to trouble-shoot because you can only trouble-shoot when they break.  Do you have an multimeter?  How easy is the spark plug access?
Let me know.
Eric