I had bought the pump for the lower gear oil in my Johnson 30 outboard.
Never bothered to try it on the Mercury BigFoot but this summer was curious about the lower unit on my MerCruiser 3.0.
Fits fine, but after reading the manual once more, found that there is reservoir bottle in the engine compartment for topping up....on the opposite side of the engine oil filler and the power steering reservoir bottle. Now it's really easy to check on all three.
I will get the dealer to do my winterizations as long as there is warranty on the motor. (5 years)