As you know Bach is making their lead pipes out of yellow brass. That leads to the “red dot” problem. I’m sure you’ve already seen a lot of them.
What are those red dots? Yellow brass is an alloy of copper and zinc. Because of the corrosion the zinc evapurates until there are little holes. You can try to clean the instrument on a regular basis but mostly it won’t help forever. What can you do about it?
A modification here in my workshop includes a new red brass lead pipe without any corrosion problems… Your instrument will have an extra free-flow effect and instant feedback while playing in addition to a warm and compact sound.
While working and soldering on your instrument, I’ll check the other parts for red dots and replace them if there’s a problem. You can get a new surface lacquered or plated, valve alignment or smaller configurations as well.