Blue leak found at the base of a gas furnace. Doesn't appear to be recent. Any idea what this is(02)

Blue leak found at the base of a gas furnace. Doesn't appear to be recent. Any idea what this is(02)


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Blue Leak Detecting Fluid Stock Photo - Download Image Now - Architecture, Backgrounds, Blue Methylene Blue Leak Test Method - Leakage Tester Blue leak found at the base of a gas furnace. Doesn't appear to be recent. Any idea what this is