Sal,
If you never carry passengers it's probably OK. If you do, think of a container of 200 deg liquid under 40 or more psi with fittings on it that could drip/leak nearly in their laps...
Unless one races on tracks, there's seldom a need for one-I bought and mocked one up 5 years ago and decided against it. The motors been fine on
synthetic and starter notor Pre-oiling.