Has anyone ever tried a leadpipe swap on a miraphone 186 Bb?

I recently purchased a used Miraphone 186 with 5 valves. The fifth valve is added later and the leadpipe doesn't seem to be the original. It's in excellent condition and has that typical German sound with great projection. But...

The only problem I'm having now is that some low notes aren't really working. It's like there isn't enough space in the instrument for the amount of air I want to use. Low Bb down to Gb, concert pitch, feels restricted in air flow. At louder dynamics the sound breaks.

I also own a Yamaha fiberglass sousaphone and a Musica Steyr Bb kaiser tuba. On these tubas the low register from Bb down works just fine.

Would a larger bore leadpipe fix this?

Has anyone here swapped a leadpipe for a bigger bore leadpipe? Why did you do it and what were the effects?

Senior high school student. I’ve been playing the tuba for about 4 years and have loved every bit of it. I realised that i’d love to continue playing as a career whether it be teaching or as some sort of orchestral musician. However my other subjects are making me feel sluggish and not motivated to do anything, sometimes including practicing. It feels like i’ve hit a plateau and i could be doing a lot better.

Once school finishes i’m definitely going to go to university and continue studying music, but until then how do i keep myself going? I love playing so much and music is the only thing i want to do. Maybe this is more of a rant, but i’d love to hear some advice or stories of you guys’ high school life as tuba players.