I bought an old house built in 1951. The heater needs to be replaced. There is no AC. I plan to get new heater/AC. The dust piled up inside of the air duct. I can see that asbestos dripping down the duct at least at one place. Should I clean the old duct and fix it where it is brokn? Or should I hire a professional abatement specialist to remove the old duct and put a new one? Which way will minimize the risk of the exposure of abestos for me and my family? Thanks.