I have a Water Furnace Premier from 1992. Yes, I know it's old. I've replaced compressor and fan motor in the past four years. A week ago, we noticed A/C couldn't keep up to set temperature; Stage 2 on all the time; no fault lights. Local WF dealer says the Coaxial Heat Exchanger has a leak. He said the part is no longer available. He recharged the A/c; total cost $473. Six days later, it's doing the same thing. Tepid cool. Set at 74 degrees and at 10:30 in the morning, it's only cool to 75 degrees and at Stage 2. First, I don't feel I spent $473 last week very wisely. Secondly, is that part REALLY no longer available?