gogboy

Hey guys.
i have recently purchased my 4th X6,easily the best one I've had,its only covered 31,000 miles and it runs like a dream,the biggest difference I've noticed is the fuel consumption for instance with all my other three i got between 300-350 miles out of a full tank but I've just hit 300 miles and i have a quarter of a tank left! so I've easily got at least 100 miles left. Naturally i want to keep this car in tip top condition so im putting it in for a big service in a couple of weeks but im going to provide all of the parts eg plugs oil ect. Was also thinking of getting the gear oil changed as well but when i look at the owners hand book it didn't say i should change it,just inspect it? i rang my local Mazda dealer and they didn't know either!!! (we dont have enough experience with these cars he said) so is it worth doing the gear oil you think? thank you very much for any advice you guys can offer.