Given that the Plutonium power core is putting off 2000 watts of heat in order to generate 125 watts electricity, I find it surprising that they don't have enough heat to keep wet-lubricants heated sufficiently. But - that's an awfully big Rover, and it does get pretty cold on Mars...
2000 watts at 14 years in kilowatt hour - 245,000 kilowatt hours.
Remember, it's got a 14 year lifetime because the half-life of Pu-241 is 14.1 years. At the end of that time, half of its mass will be gone, and it'll be producing half as much heat. It won't produce a steady 2KW for 14 years and then bing, go out like a lightbulb. Power produced will slowly fall over time.
You mean, half of the plutonium mass will be gone. It will be almost completely be replaced by other elements. Though I don't know how much energy they give off in radiation, or whether they are stable.
2000 watts at 14 years in kilowatt hour - 245,000 kilowatt hours.