WD-40 isn't a lubricant. PB Blaster is much better for the job you're trying to do. Liquid Wrench is another similar product.

I've used a 50/50 mix of acetone and ATF for years and it's better than both. The disadvantage is that it isn't in an aerosol can. if the manifold is off the engine you can probably get it into whatever cracks and crevices necessary.

1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)