Faster discharge on cloudy days may exactly mean that they are close to being dead. "Reserve capacity" by definition is the capacity at 25A, and with your devices you are not drawing that much. What you observed on cloudy days in absence of proper charging current, is a faster discharge due to reduced total capacity - not "reserve capacity". Now, Concorde recommends conditioning when battery capacity drops by 20%, if memory doesn't fail me. So this should be done. With your energy needs being so low, you can keep this battery - who knows - maybe few years more. Other people would have thrown it away already because their energy needs are higher and sunny hours are fewer.