F90 Oil Leak from Drain Plug

I've got an 06 F90 that slowly leaks oil from the drain plug. I've tried tighting the bolt a little more, but don't want to go to tight. Should there be a rubber washer or anything on the bolt to prevent the leak?

There should be a washer gasket with the lower drain plug. The upper plug does not.

I guess I should have stated its a 4 stroke and this is the upper drain. So what do you suggest to stop the leak?

hello, according to my local Yamaha tech, there is a paper gasket with that drain plug. He said to be very careful in tightening it due to the aluminum casing.