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I've had my pt-20p for about a year now. It came with the original tuba world gig bag that's probably about 10 years old. I always had troubles closing it and about a month after I got it, my zipper busted. I just paid $25 to have the zipper fixed, and I slide my tuba back in the bag, try to zip it and it busts again! Has anyone had this problem with the bags that zip around the bell before?

Get that zipper replaced.

I've had some bad luck with some cobblers (instant failure), mediocre work from others (held for a year), and excellent (still holding after many years) from another. The cobbler I used was an excellent leather worker and I impressed upon him the importance of a burly heavy duty zipper that won't bind or fail.

So, I'd recommend finding a solid shoe/leather/outdoor gear person with lots of experience with a variety of products (and not a seamstress) and ask for the best quality heavy duty zipper.