I changed the diff oil today in my FG MKII Turbo ute, I used Castrol syntrax 80w-140 full synthetic. I loved the smell of the oil. But later on I had a look in the service manual and found the service intervals for the turbo utes, very short ? every 7,500km, and also noticed there should be some friction modifier added. Is it really needed ? Or just an old wives tale ? Pics of the service manual pages below.