My Adult Son Lives In Korea And Has Often Had

My adult son lives in Korea and has often had wax and infections in his ear with exposure to water. He now has been having "eustachian tube dysfunction" for a couple of weeks - as they have diagnosed it in Korea, with the symptom of fullness, like his ear hasn't "popped" after coming down from a flight. What else can he consider? He does fly often with his job and one of his favorite hobbies is diving - both concerning whether or not he should continue. Can you advise please?