Im no ace tech, so when i ask ?'s it's in the spirit of learning and troubleshooting... so what are you thinking about oil and debris buildup on cooling fins? I only ask as with daily use and living in a dust bowl, probably all 4 of our mowers look about like that? If any ever had spills/leaks we pressure wash but... are you ssying their is some sort of shut down occuring due to a safety "overheat" feature??? Isn't that small heat sink in the photo, a voltage rectifier of some sort? Any help appreciated... again weve resolved simple seat switch failures and things but not certain where to begin as (A) this mower has a few- pto safety, the actual pto clutch, a parking safety, and i think one other safety shutdown and with the issue being so random/ intermittent after hours of use im not sure howntovtest/re create