A leakdown test determines how well the valves and rings are sealing. The engine does not run during a leakdown test & is thought of as a reverse compression test. Results are usually in % (below 20% is generally good). To say it shows a cyl misfiring makes no sense.
See here.
Run do not walk.
The ignition is a waste spark system where two plugs fire at the same time, but with opposite polarity. #6 & #3 are on opposite sides of the same coil. If there is enough cable, switch the two to opposite sides and see if the misfire follows the change. What did the leakdown show?