Re-oil leak in my IO 360:
Found by washing engine carefully (no water in mags or dry vacuum pump). eg simple green with hot water.
Run engine short time, because I want to see where oil emanates from before it spreads out too much.
Examine with quality Ultra Violet light: there it was from front seal. Could NOT see it with naked eye. Replaced seal. Retested, no more leak.
Used Slim 3W Penlight (100 lumens), Model SNLSM3WW13, $60, from Sunlite Science & Technology, 345 North Iowa Street, Lawrence, KS 66044n(785-832-8818).
Works good... last a long time.
Also, Snap On sells a very similar light.