[InFlight]

Miter and Bevel Gears require fairly tight tolerances to avoid excessive gear tooth wear. These Gears mating at an angle do induce thrust loads.

Skipping the inclusion of a $1 bronze or brass thrust washer is fine if your design, machining, and assembly tolerances are close to perfect. However, repeatable perfect machining and assembly don't seem to be a common characteristic during a rushed build season.

The thrust washer both distributes the thrust loads, and also provide a less hard wear surface between the steel gear & steel bearing. This is simply good engineering practice for use of these gears, your welcome to use it or ignore it.