I think the idea of flashing the firing system is more valid on percussion guns that often have a far more convoluted flame path from cap to charge. So blowing them clean by popping a cap or two is a fine idea. On a flint lock it may actually be making things worse since the flash of the pan and low pressure from being out in the open could result in fouling plugging the hole. This doesn't occur during firing a charge because the pressure leaks out rather strongly when the main charge burns. So I'm thinking that flashing the pan is going to hinder more than it helps. Far better to patch and wipe away any excess oil instead.
