that would be where i start. If you plan on pulling the motor i might suggest more thing while your at it. Might want to think about the timing belt, tensioner, water pump, ect. General maintenance things that are just simply to replace while you are in there.

 

It's still only 40 psi total. I'd still rec he do a leakdown test. Might save him grief later. At the dealership level we do a lot of leakdown tests to verify which direction a tear down should head first. Warranty pretty much demands it. It's a quick and simple test that might show something else is wrong. Might have a broken ring land and the piece of piston caused a slightly bent valve. We see it all the time. I've had busted piston pieces clear up behind the throttle plate. Guess it just depends on how you are approaching the job.