Correct gearbox oil for 6 speed 1.33

[Fungus007]

I've ready a few post here that the factory recommended oil to use is the  2.5 liters of SAE 75W GL-4 monograde full synthetic and putting in multi viscosity oil will cause long term damage. 

However the only mono grade oil 75w gl-4 oil I could find is this brand called SWAG and doesn't indicate whether its full synthetic. 

So my question is should I go with a know brand like Red Line MTL 75W80 GL-4 or Penrite 75w85 gl-4 full synthetic or the Swag brand? 

Mt gearbox is also making a slight whirling sound at highspeed between 80/85km/h so maybe in my case having the multi grade thicker oil at normal operational temp is good? 

 

[Mark_P]

The Safety sheet doesn't say if it's full synthetic - https://cdn.pkwteile.de/uploads/hazard/passports/2128211-EN-1.pdf

Autodoc does say it's compatible with the IQ - https://www.autodoc.co.uk/swag/2128211

The swag website swag.de doesn't say anything either.

Edited 2 hours ago by Mark_P
added more to the post