My Serial Number is OC 186507. According to the chart at:

http://www.maxrules.com/Merc_model_files/40-50.html

O = Oil injection
C = Counter Rotation

What does the counter rotation mean?

Cannot definitely identify year from this chart, but found it (I believe) on
another chart gained by Googling.

Also, I cannot find any OC's in this chart. I had to climb behind this boat
with a flashlight and wipe the dirt and oil off the SN tag. I KNOW I got it
written down right.

Thanks for bearing with a noob.

Steve