GL4 or GL5 Gearbox oil

[api330]

Sorry to go on about gearbox oil but i am struggling to find out the spec of the oil for my z4m gearbox (same as e46 m3 manual) I know the grad is 75/90 but cant find weather it should be a gl4 or gl5 and should it be a fully sync oil or a normal oil, Any help will be greatfully received, Thanks

[CarbonM5]

Try Royal purple syncromax,it makes the shift nicer.

[api330]

Any idea what spec it is, I have heard of this stuff but can not find the spec of it, Cheers