year and make of my mercury motor

[smokercraftsman]

I have an older 15 HP mercury 2 stroke and i can't find any serial numbers any where on the motor to order parts. I found a number on the freeze plug and read some where that it could be traced to find what year this motor is. is this true? the number I found is B316853.
any help here would be greatly appreciated. I have to replace oil seals in lowwer end, oil is milky white

[cisco2238]

This is the serial number