I have a 50 year old porcelain tub with a broken drain linkage. I cannot unthread the drain with a drain tool and strong pressure with a crescent wrench or a large screwdriver through the holes in the tool. Can anyone help. Do I have to use acetylene torch & heat it up and if so how do I prevent damage to the surface of the porcelain? Thank you, David

Do you have good access to the drain from below?