The Sidewinder ROV is very simple it is just a plunger with a spring on the back side, once the oil tank builds pressure the plunger is pushed and the pressure is relieved. That means there is always some pressure in the oil tank. It really doesn't do much good without a tether. I saw first-hand a sw rolled over and the throttle got pinned, oil made it to the air box and into the engine which created a monstrous plume of smoke. Not good.
I disagree that it was made to come open to clean. That might be a good idea but I would want a snap ring or something for a retainer, not just press fit!