Oil Change for 15 HP 4 Stroke Motor

[Ballingbob]

I have a mid 90's Johnson 15 HP 4 stroke motor that I want to change the oil. Does this motor have a drain plug or should the oil be sucked from the dip stick?

Also, I'm trying to get the casing off and have taken all of the screws out (all that I know of and can see) and the casing won't come apart near the water outlet on the back of the casing. Are there any hidden screws or latches to get the casing apart? It will open from the front but I don't want to pry it in the back for fear of breaking it.

Thanks for your help