Once I saw someone using a spark plug for a sealed connection through a vacuum chamber. Maybe rhat is simpler than making your own.Great blog with great projects you have.
Anonymous, yes the spark plugs work great -- especially for high voltages. In this case, I'll need to conduct over 100A, so I'll need a fatter conductor to carry all of that current.
If you use Apiezon instead of the typical DOW vacuum grease then it can be removed with acetone. It is more expensive but you really don't need much anyway. The DOW stuff is basically insoluble.
Don't use grease, any kind of grease, new/good o-rings don't need it