The one I tried years back also had that 3rd partial. As did the Fasolt. I don't look at 25c to be much though on any tuba, especially not this size

It would equal 4 cm on a tuning slide, but alt fingerings usually solves it.
well of course. Less is a great bonus. Crossing my fingers.
As for the leadpipe....changing it is fairly easy giving it is a 2 pice thingy
Not the first thing I'll try, but done it on most tubas already, so I guess it might happen
And yes. This is the one Luc had.