What space probe / robot has sent us back messages for the longest period of time?

Both Voyager 1 and even Voyager 2 (after an error change just one bit in the programming, NASA was unable to decipher its information, even though it was still able to send it. This has just recently been corrected) are operational and still transmitting. They are also the furthest man made objects from our Earth. Both are approaching heliosheath, the area where solar winds and interstellar gas begin to mix. Just one layer away from reaching the heliosphere and then true interstellar space. It will be a long time until that happens but the Voyagers have far out performed their expectations. Having been launched in 1977 to explore the outer solar system, specifically Saturn and Jupiter, it has churning out scientific data for over 33 years.