I have a 1981 165hp In-Line 6 Mercruiser. I am rebuilding the trim/tilt cylinders which happen to be of the Alpha generation. I flushed the reservoir by pouring oil into the reservoir and letting it run out the trim cyl hose. What is the best choice oil for filling the reservoir? I have 2 gal of high quality 10w-20 Hydraulic Oil. Is this a good choice or is it too light?