Holden Trimatic / TH180 vacuum modulator (new /adjustable made in the USA) is known for leaking internally or allowing oil up to the manifold.

Adjustable range: 66-75 kpa

Do not use the factory gasket as they create leaks! (25 years experience in building transmissions)

Use 3j permatex (form a gasket the brown-gooey stuff)

just on the thread.

suit 4cyl, 6cyl, & V8