650 mL is the recommended amount of transmission fluid.
1 mL = 0.00105668821 US quarts
So 650 mL is 0.6868473332305001 US quarts. 2/3 = .666666666 ∞
SOOOOO, drain out the transmission and fill it with 2/3 of a quart of fluid (either 10X30 motor oil, ATF, or some sort of gear save gear oil, whatever you choose).
A leak down tester is a device which blocks the exhaust port ensuring an air tight seal, pressurizes the intake boot to a desired amount of pressure, and then has a function to track pressure loss.
Usually an expandable rubber plug for the exhaust port, a PVC adaptor in the intake manifold with a small piece of hose and a low pressure gauge installed with a schrader valve to add air from a bicycle tire pump.