Hello, Normally Rheem’s serial number has a date code built into it, but yours isn’t fitting the normal style. Clearly yours is an older unit and has had flame rollout problems, but I’d call Rheem at Customer service: 1 (866) 720-2076, and see if they can help. At a minimum, you want to fix the flame rollout, and check relief valve and anodes. The plumbing around the tank is a mix of copper and steel, which causes problems, and the gate valves should be replaced with ball valves, which will make managing it easier. Hope that helps.