I just drained the gear oil out of the bike as I have to strip the engine to rebuild the crankshaft and fit a new rod kit.
I used the Flowstick to see if the old oil was still within viscosity limits after about 350KM of use. I put the old oil vs a sample of the new and the old has just lost its viscosity a tiny bit perhaps due to the churning and chopping/shearing forces of the gear teeth.
But it is still within serviceable limits, but wont be reused again.
The oil has darkened considerably due to the heat from the engine and the friction between the clutch plates making the red dye discolour and from clutch material contamination.
The red dye used is the same as what is used in ATF which in Automotive use stays reddish pink for 10's of thousands of kilometres but the severe service of a 2 stroke dirt bike kills it within a very short time. So it pays to change the fluid regularly. The oil was as dark as old 4 stroke engine oil but still had that sweet GL4 scent of its additives.
