Lu,
I e-mailed you some more info but I like your static discharge idea. We also occasionally see arc spots from lightning strikes on the main gear sleeves, so it could be lightning rather than mere static that initiates the hot spots. You can't ground an aircraft parked on the ramp in these parts and we do get some fearsome electrical storms. I'll feed that idea back into the data that we exchange with Boeing.
**********************************. .Through difficulties to the cinema