Did he try a really strong magnet to pull up metal that can't be reached? I don't like air pressure because it blows the object into the machine sometimes. I am not familiar with a Brother but my machine has a bottom plate that unscrews. After that is undone --most scrap and fuzz can be shaken out the bottom. Don't be afraid of your machine. My Futura has a plastic bobbin case. Everytime it piles up the needle damages the plastic case making a rough spot on the outside. This will catch the thread and won't sew smoothly or in my case it was not at all. I have to sand the edge smooth or buy another bobbin case. They are $16 but I would pay a good price for a metal one.
I think in order to be a good sewer or artist you must also be a mechanic too. When it comes to handing out money to clean up my machine, I always say "I could have done it myself and been more satisfied. If I need info , I google the internet and usually a techie will have had the same problem. I'm always amazed at the tutorials on You Tube.
I just learned how to install a clutch cable. Yes, I'm taking it out to be repaired. (it's too cold to be under the car this time of year.) BUt I know what he is going to do and there will be no surprises when the bill comes.