Pat,
Johnson and Evinrude used two types of plugs. One has a flat plastic washer and the other uses an o-ring in a recess under the screw head.
The plastic washer should be replaced every time. The o-ring can be reused, but it should be replaced if it looks flat.
The washers and o-rings should be bought at a dealer (buy enough for the next oil change too) and don't gamble on unknown parts. While at the dealer, you can buy a couple of spare plugs so if a screw slot gets damaged you have a spare. Buy the same type as you removed. DO NOT put a plastic washer under the head of an o-ring plug!
You can change the washers by removing the lower plug, screwing in the pump, remove the top plug, change the washers, top up the oil, reinstall the top plug and then the lower plug.
The o-ring plug should be torqued to 60 to 80 inch pounds. The plastic washer type should be tightened with the large screwdriver.
These instructions are specific to Johnson and Evinrude.