Just found the part in the 400/4 parts list described correctly, unlike Haynes, as 'piece, oil lock' with part number
51432-369-000. Is that your part number?
Checked my early 350/4 parts list and they are a different setup, apologies to anyone if I misled you by saying 350 and 400 are the same - they ain't.
Ian
Just found your part number for GL1000
51432-371-003
So they are different size but similar in appearance