It's worth learning how to check for leaks with a leak light. There are some common problems that kill some notes. Bb not closing properly is one, G# is another. And even a small leak can make a sax unplayable. And don't forget the neck - leaks there affect many notes, but don't show up with a leak light. Just because the neck screw is tight, it doesn't mean the neck is sealing. The screw is there to hold the neck on, not to make it seal. And overtightening the screw can cause leaks as it distorts the tenon. Not to mention snapping the screw.