Need thermocouple for Aquastar on-demand hot water heater

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I have an old-style Aquastar 125 on-demand hot water heater with a standing pilot. The unit has performed flawlessly since its installation in 1997, and supplies hot water even during Maine's frequent winter power outages. My problem: the thermocouple is on the way out and is living on borrowed time. Was wondering if anyone either (1) had one of these units lying around from which they are willing to sell me the thermocouple, or (2) knows of a work-around for this problem. Is there such a thing as a universal thermocouple? Thanks so much.