Changing from a high viscosity oil (15w-40) to a lower viscosity oil (10w-30) can absolutely cause more oil to leak from existing orifices.

When I switched from 10w-30 to 20w -50 oil in my Cadillac, oil leakage was cut in half.

Why did you change the oil type and the viscosity in the first place?

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)