Really, I thought it would have been power steering fluid. I can get 20W, or I can use 10w30. Does it make a difference? Figure that is better than the $8 a quart for mercruiser fluid.
Good luck finding any 20wt. I ended up using 10w30 in mine. I don't know if you can read it in the picture or not, but here is a shot of the manual for an older model than yours.... it suggests 20wt oil. I don't know if yours is the same or not.