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Nobody will care what the tuba looks like.

Your most important first impression will be the tape or cd you submit for the highly competitive first round.
These recordings allow the audition committee to select those that they want to hear in the live rounds.
Once there, you will need to nail the excerpts and your prepared piece (assuming that one is required) and show your ability to sight-read.

Again, nobody will give a thought as to the horn's appearance.

Best Wishes and Good Luck to all auditionees!

Tapes aren't due until Jan, which means they need to screen and wean. The audition probably won't be until April the earliest, but I'm not in the band, so I don't know their timeline. Just conjecture on my part. Plenty of time to practice and get your horn fixed.