Hi
What oil are folk using for their gearbox, mineral old school, or semi synthetic or fully synthetic?
to avoid clutch slip
Cheers
Gary

Pick your poison.  JASO MA rating is a standard you can look for.  JASO MA2 oil has the highest friction rating.  They come in all varieties from relatively inexpensive motorcycle specific engine oils (or I've used Shell Rotella diesel oil) to high-end (expensive) boutique full synthetic gearbox oils rated for wet clutches.

The (arguable) problem with most regular engine oils are mandates (in the thinner grades) to add slippery energy conserving additives to save fuel...  anti-friction additives are probably not good for clutches.

If your clutch is slipping, it's likely adjustment or wear...  an oil change is not likely to fix it. 
 

The old owners manual says to use 10/30 motor oil, but I know modern oil has all kinds of friction additives, so I've been using Yamalube 20/40, and it seems to work well with the wet clutch.

www.amazon.com/gp/aw/d/B005BH9OB8?ref=ppx_pt2_mob_b_prod_image

thanks Guys
I dont have any clutch slip, I want to avoid it by putting the right oil in it.
Ive got an order going in to Yambits for a r/h side cover gasket as sprung a leak and seen this oil. wondering if anyone used it
yambits.co.uk/dt400-silkolene-gear-oil-l...-litre-p-133053.html