Convert Hinge Tube to Pivot Screws
This is a common modification on vintage horns because they tend to have single keys mounted between posts on long rods. The benefits of converting the key to pivot screws are that the key can be slightly bent and still function, and it's easier to maintain.
If your low B and low Bb share a hinge rod, or if your low C# has a hinge rod, you are a good candidate for this conversion.
On the bari shown here, the low B and Bb shared a very long rod. Now, each key is mounted by itself on pivot screws.