You should try Vamoose, it works!!!!!!!
The AC duct's are in multiple places in the home. The main duct would be on the main floor where the air conditioning can keep everything cooler. The duct is located on the floor in the main part of the house.
I don't think it is coolant. It is just condensation caused from high humidity and the cold air. If it is coolant it should get on the floor and you should loose coolant.
Change the filter and clean the coil. If it smells like a dead animal clean your duct work.
I am not sure about ac Moore but I know you can get it at walmart
The duct work probably runs through an area that is hot and humid, i.e. attic space, and it isn't insulated.
replace? why not fix it?
Check your duct work in your attic. Heat from attic could be coming in through a broken connection or hole in duct work, especially in a house that old.
14" Round or 14" x 12" Rec. will work.
some AC duct is made of insulation wraped in foil it could be a number of things ei. old duct to rodents
under the glove box on the duct work of the ac. there should be a small tab to push down.
The safe answer is, "you don't" however if you must, you should seek guidance from a structural engineer with a residential construction background.