Rongawer, the O-ring idea might do the trick for me, thanks.
However, I just can't tell what series my winged studs are. I know they are stainless, and have a -4 on them, but I'm wondering if it matters whether they are 2600, 2700, or 4002 series and whether I should use the retaining split washer or the solid internal tooth washer. I can see how the split washer allows the stud to be loose while reatined on the oil door, but maybe the solid washer would be better.
In the meantime, I'll try the O-ring idea.