10W40, 20W50, SAE30. Anything goes here. Change my strokers gear oil once per year, meanwhile just watch 2 things carefully; 1. the level[so you make sure it is not leaking out, and 2. that your gear oil is not turning a condensed milk colour[that will mean that the waterpump seal is letting coolant fluid into the gearbox cavity.
Apart from a kickstart idler gear on a PE175, I have never had problems with any Japanese bike gearbox. I of course know how to treat them.

You engage 1st gear, you do not "kick" at the gear lever with your trendy fat MX boot.