Couldn't tell you specifically which side (or center), but the unit is always (as far as I've ever seen) mounted somewhere near the transom, if not onto the transom. Just start opening hatches and you should find it - it will be accessible. BUT, what do you mean by "failing"? Since you haven't yet physically laid eyes on your pump, I'll assume you don't know if it's low on fluid. It shouldn't be unless there's a leak. Do you have any evidence of a leak on the outside? Check for leaks (inside) not just at the pump, but follow the lines to the nipple that goes through the transom.
