I use the high temp red grease "certified for use on European vehicles"
Just a little blob about the size of a peanut right where the 2 gears mesh to each other.
No need to spread it all around the gears yourself. They will do that for you while you ride down the road. I most likely over grease them by how often I do it, every other ride. To me it's cheap insurance. Just wipe out the excess grease that gets flung off from inside the gearcase with a q-tip when it gets built up too thick. Sometimes I re-use the flung off grease to lube the gears, it just depends on my mood at the time.