The Service Manual and Owners Manual say: Replace every 2 years
If the dealer said anything others: rtfm
I don't think that it is really necessary or very important to change the oil but this are only 2 screws and a few minutes work and a little bit oil... Why not? I couldn't be false
btw, i visited today my dealer and bought the sealing washer for the drain and fillport and will change the oil tomorow. I will take a better oil than the original one (with MOS2), this also can not be bad