Weight of the fluid you use depends on the manufacturer. For example, one company’s 10W may be another’s 5W, so check this first. I used Silkolene RSF 7.5 for my RR8. Really good stuff and set to the specified air gap. Don’t forget to change your fork oil seals and check the dust seals and bushes at the same time - genuine best. Got my seals from Brooks suspension.
This is what I used to help: https://transmoto.com.au/comparative-oil-weights-table/ Honda 10W fork fluid is 35.2 Centistoke (cSt) at 40degrees C. Look for fluid with a similar value. Generally the higher viscosity index (VI) the better, as this means fluid viscosity remains stable under temperature changes giving more consistent damping.
