In the 1960s when I worked in a service bay I was told to use the copper washer on the engine drain plug if fitted and for the rest of the engine, gearbox and back axle just nip up the drain/filler plugs. No fancy sealants, never had any leaks. Back street boys?
The drain/filler plugs without washers are usually slightly tapered so they lock in when tightened. I never used a sealant.
