By Ken Hoke, Plane Owner
Buy an inexpensive black light flashlight to trace Piper oil leaks and seeps. There are several options available on Amazon.
While researching an oil leak, I found this tip in an old AOPA article. Engine oil fluoresces when illuminated with a black light in a dark hangar. There are expensive oil additives to make the oil glow brighter, but I found that the oil shines plenty bright by itself.
With light. 
Author’s light looks like this. 
Without light. 
With light
