According to NASA, the rovers 'Spirit' and 'Opportunity' have lasted more than 20 times their initial three-month mission plan, with each suffering from aches and pains associated with their longevity.
Sigh. Growing old is a bitch.
It went to the cafeteria at 4:00 pm and forgot where it parked the car.
FWIW, the 3-month mission plan was based on the expected worst-case power degradation that might result from dust buildup on the rovers' solar panels. The arrays have stayed surprisingly clear of dust (there were articles about how something had apparently cleaned them off, a couple of years back).
The electronics, sensors, etc. are space-rated, and would be expected to last much, much longer.