I'm curious to know if anyone has a solution to the crack in the wood.
I would suggest the following:

1. Do not use a heat gun to melt the shellac.  Shellac doesn't melt,
but lead does.  Shellac is dissolved in alcohol, but if it's brittle
remove it and reseal.

2. Fill the crack with epoxy, then seal it all with shellac.

3. Replace the lead tubing as needed and re-shellac to seal it all.

Eli Shahar
Sonora, Calif.