Best gearbox oil to use 1.8 vvti Avensis

[Ebob01]

So in a few months I will change the gearbox oil in my 2008 1.8 vvti Avensis. 

It will have done around 115k by then, the previous owner changed the gear oil at 70k using Castrol syntrans multivehicle. 

Sometimes the gear stick can be a little stiff and it can be a little notchy but nothing to worry about at all really. 

My friend has the exact same car with 60k on the clock and I drove it and the gearbox feels much slicker. The person they bought it from always had it serviced at a Toyota/Lexus specialist. 

Also mine sounds a little bit louder (almost very slightly gravely) when revving in the lower gears but I don't know if that could be the condition of the exhaust or even just a bit more engine noise, certainly nothing to worry about though.

I was wondering what the best gear oil to use would be? 

I have seen good things online about Redline mt90 however I have also read stuff  saying the gears started grinding when shifting and people said they had to take it out.

I'm wondering if it ain't broke don't fix it and maybe playing it safe and using some 'normal' gearbox fluid maybe Mobil 1 or something....

I might be getting a small lightweight caravan next summer so maybe something a bit heavy duty to protect the box....?