Thank you jay_bob!

If vacuuming doesn't work, do you know if the prechamber can be removed, without removing the valve cover (using a slide hammer). It looks like it's maybe possible, but I've never done it - so thought I'd ask?

Also, On YouTube a technician says you never want to take one of these heads off, since it's difficult to replace without having head gasket leaks. Do you know if that is actually true? I read many posts here that people have taken these heads off for various reasons. I don't read anywhere that they have problems with them afterwards...