R33 Gts-t Gearbox And Diff Service

[TUF250]

hi all I have a 33 gts-t with 86000 on the clock and would like to change the gearbox oil and diff oil not because there is anything wrong but because I like to change all the oils when I get a new car.

I was going to get the synthetic nulon 75w85 ($29.99 per liter) but everyone here recommends vmx80 which is much cheaper. castrol recommend vmx-m 75w85 or vmx80... someone said nissan run vmx80- from the factory is this true? i dont want to run a mineral if there is syn in there already thats all.

also the castrol website says 2.8 liters... is this wrong is it infact 3.8 - 4? can you overfill it?

in relation to diff the oil manufacturers recommond hypoil oil. I think I will run Nulon LSD 90 as it covers lsd and non-lsd types. what do people think of the 90 weight? good choice? things like 85w140s would be too thick surely?

now i thought that in stead of using the expensive synthetics at $30 a litre, i would use quality mineral and add the nulon G70 into the box and diff which everyone seems to rave about, this will work out much cheaper. how does this sound?

thanks

Jason