Mercury - Transmission Fluid Filter Kit Hurth 630 & 800 Series Canister Style Filtration 879194241. Overview. Anyone who has spent time around inboard or v-drive boats knows that a healthy transmission is just as important as a smooth-running engine. When the gears bite cleanly and the shift engages without hesitation, the whole boat seems to move with a quiet confidence. But when the transmission begins to feel sluggish or chatter under load, it steals the fun right out of the day. That is why