The plastic oil filler plug just broke off when I tried to check the oil on an old Briggs and Stratton motor. Just the top part. What kind of thread does it have? Pipe thread? If so I will replace w/pipe plug.
Go out on your town's dump/recycling/trash night.
There's gotta be a tossed lawn mower from which you can grab the oil fill cap.
Maintain your mower's "Concourse d 'Elegance" status!