tac foley
Registered
As David says, the dome's construction looks similar to that of Accucraft's Sea Lion: on that loco, the top section is threaded onto the SV housing, and closes onto the lower section of the dome, which is a brass pressing/spinning. If it is similar -and if I remember correctly- the penetrating oil will need to go just inside the aperture at the top of the dome cover. The joint where the paint is, is merely a butt joint, and is not threaded.
I hear and obey. Copious amounts of le huile-penetrant are, even as I write this, seeping their lubricious way into the recalcitrant threadments.......