You already know that it is a waste of time and money to play on a faulty instrument. A leaking instrument will not respond appropriately, will not produce a full sound, causes intonation problems, etc.
You will spend time learning to control your airstream better. Unfortunately, air is invisible and thats why you often cant see the problem.
Being unaware of the cause of the problem, you will end up wasting a lot of time trying to overcome and compensate for problems caused by the instrument. You might also try to solve it with different mouthpieces, ligatures or reeds or even a more expensive instrument, but instead of eliminating the problem, you will end up wasting more money.
Whatever you learn on a fault free instrument, you can transfer to any other instrument and it will work. If you need to learn awkward trick to do that, they might not work on anything else.
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