Squirting any liquid around a suspected leak should make the engine operate "differently" if there is a leak. A combustible material (propane for example) will increase the speed if there is a leak. An oil may smooth out the engine, but not increase the speed if there is a leak. Kinda' depends on whether the engine is already rich or lean.
I mentioned the distributor issue because I ran into it with a 4 cylinder engine with a worn cap and rotor. It would not idle properly, but smoothed right out when speed picked up. In fact it smoothed out when you pushed the distributor cap sideways. May have even had a slightly worn distributor, but the new cap and rotor fixed it.
