You mis-understand how these motors are put together.----The rectifier mounts directly over the water jacket.----There for it uses a gasket , 0350357 is the part #.
The rectifier sits on top of the block.---It is water cooled.----Therefor it has a gasket.-----Are you pushing the key in and holding it in while cranking it over for cold starts??
Take a boating safety course.----Read an owners manual 3 X and read some books on boating.---It is much easier to get into trouble on a boat , then to get out of trouble.-----Things go wrong quickly when they do go wrong.-
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???-----Drill into the exhaust housing from the side.----Start with a 3/16" drill.----Drill close to the block.----Get oil in there.-----If this fails go to bigger drill to cut the stud.----Been there done that.
Point gap determines the timing.----Now if you want to do a first class job you can use a meter and timing marks to set the points to open at the exact time to get maximum spark.----Many U-TUBE videos explain this simple procedure.