The iboats store lists maintenannce manuals, but I cannot find the correct one for my friend's motor (that I am helping him with this week).
It is (I believe) a 1987 model. 45HP inline four, s/n is 0B2051XX.
The closest available manual is:
Mercury Outboards, 40-115hp, 3-4 Cylinder , 2 Stroke...