Tuning bits for Besson sousaphone

[mjp]

I have a Besson Brevete (as engraved on the 2nd valve casing) Eb sousaphone that I need to get at least one tuning bit for. It plays extremely sharp, but I do only have one bit that came with it. I'm not sure if what I have is even the right bit/neck combo, or if the pieces are just dinged up, because it does leak. After a bit of playing, water droplets sneak out from between the neck and bit. I'll try to post some pics from the phone later...

Does anyone know what bits would work on this instrument and where I might purchase them?