I have been chasing an oil leak for a while on my Franklin. I happened to attend an IA seminar and become acquainted with a Continental Engine Rep. He was discussing troubleshooting oil leaks and explained a technique that I thought about but was concerned about damaging the seals on the engine.
I may be telling everyone something that I just did not know but he uses air pressure to test the crankcase, accessories, intake and exhaust manifolds.
I removed my short stacks and used 2 inch rubber expandable automotive freeze plugs to seal the exhaust. Removed the carb and installed a 2 1/4 inch plug in the intake. I sealed the oil filler with metal tape and plugged the vent with a 5/8 inch plug.
I removed one spark plug and connected a differential compression pressure guage to one spark plug.
Solvent wash the oil from the outside of the engine. Pressure the cylinder to 20 psi and use a spray bottle with a soap mixture to mist the engine. ( the engine rep said you can go as high as 40 psi but I start thinking about blowing the crank seal.) It takes a few minutes to equalize the pressure past the rings and throughout the engine.
It works outstanding, just like checking a tire!
I found my oil leak, two intake manifold runners leaking and one exhaust.
I will add this technique when I perform annual inspections in the future to all engines.