Checking for leaking valves on the head

I found this video on youtube that demonstrated an interesting way to check for a leaking valve.  After performing a compression check and you detect a weak cylinder, you need to check for a bent valve.  Without removing the valves, there are two ways to check for proper valve seating and ultimately, if the valves are bent.  

The first way would be to put a vacuum on each intake and exhaust port and measure the vacuum.  This requires special equipment, so the video presenter offered a much cheaper solution.  Basically, spray WD-40 into the ports and look for leakage.  It’s really that simple.