Leak Around Skylight

I’m dealing with an asphalt shingle roof where water appears around a skylight only during heavy wind-driven rain. The flashing looks intact from the outside, but I’m not sure whether to start by checking the step flashing, underlayment, or the skylight curb. I found the older discussion here: https://www.rooferscoffeeshop.com/forum/topic/question-on-flat-roof

For those who have dealt with similar intermittent leaks, what would you inspect first before tearing into the surrounding shingles?