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The roughness you’re feeling while turning the driveshaft is probably because the forward (upper) gear is riding low on the prop shaft gear and the gears are fully meshed. When power is applied, the forward gear will be forced upwards separating the gears a bit. The manual mentions that the driveshaft can be forced upwards to and if the impeller isn’t free to slide up and down on its drive pin, the impeller can be forced up against its housing, breaking the seal on its lower side. I think you are OK with them and when the lube is added, you wont notice it as much.
These straight cut bevel gears are similar to spider gears in a vehicles rear end. When a rear end has limited slip clutches in it, the spiders spread under load causing the clutch packs to lock up.