So, first off, the horn I'm working with is a W. Nirschl I-800. This particular example has been a great intermediate horn, and while I do plan to upgrade to a Besson once I'm off to college, this horn is nearly flawless. Nearly.
The second valve has always been flat. Even when I first began playing, and my tuning was pretty horrid, that valve was always about 5-10 cents lower than the rest of the instrument. I've trained myself to lip it up, and it hasn't really been an issue.
Lately, however, I've been working a lot on breath support with my college-of-choice professor. It's improved my sound a lot, and made my playing much, much smoother, and tuning is generally better across the horn. But, my second valve has gotten worse. It's now closer to a quarter-tone flat, and it's beginning to be a bit much to lip into tune. An A at the top of the bass clef now sounds strained and thin, just due to how much lipping I'm having to do.
I was thinking that it could be an air leak around the valve, but I'm not sure if that'd cause tuning issues like this. The sound itself is fine. It's just flat. What can I do for the next year or two to correct the tuning on that valve?
The slide is pushed all the way in, before anyone asks