Hey all. Just before winter set in the heat stopped. Local shop replaced leaky radiator, heater core, thermostat , and by passed the rear heater core, but still no heat. The truck probably has 260k on it and came from New Mexico. It probably has never had the cooling system flush. Local shop reports “a ton” of rust each of the three times they have tried to flush it out. Do you all have any idea what else we can try?