The proof is in the pudding, wouldn’t you say?
Why were cimbassi practically extinct for so long (as in: almost nobody was using them)?
I believe for the same reason that valved (tenor) trombones aren’t that popular. Too stuffy. Which equals; no fun to play. Too much work. Also with intonation.
If ...

…..

Whenever I play I don’t hold the mpc
unless
I’m walking around (funerals and such) then I might choose to do this to protect my chops from an unexpected jolt.

Thanks for responding.
I appreciate advice but also knowing the reasoning behind it.

Sadly this is all too true. The usual solution to a slide that isn’t straight is all too often to buff it up until it slides better. Nothing like paying a repairman to make your instrument leak!

I purchased a Martin Medium sous some years back. The very surprising thing about this ’50’s horn was ...

Thanks for this.
And coming from a professional repairman I take this very seriously.

Do you know why all the tuba manufacturers (and all the sources on internet) advies only oiling the bearings weekly and the linkage monthly?

Rotaries are godly and a lot of fun to play when they are tight, quiet and fast. My 497 is an amazing ride when it’s in shape and ready to go. You only have to lubricate them about once a week so that's a major plus. But if for example the bearing plate is not just on right the valve can eventually ...

um
if this is a good tuba? A Symphonie? Then I’d leave it alone. It’s a classic horn and it’s not worth fudging it up.
Buy a smaller tuba that fits, or a cheeper one to operate on.
And if you’re really set on doing this then buy another bell to do the operation on. That way you can at least have ...

The MSP1S with normal valves (0.748-inch bore and a 26-inch bell).
https://www.sweetwater.com/store/detail/AMMSP1S--adams-msp1s-sousaphone-silver-plated-with-case
It looks the same as their MSP1TS
https://reverb.com/item/72825012-adams-msp1ts-marching-sousaphone-silver-plated-with-case

With ...

There were a couple of versions of this horn. Originally with slanted valves, they later lined them up in the vertical set-up like both you gentlemen have. Tubajug's model is the only type I've seen pictures of in the vertical set-up. The way Don's 5th is set-up is new to me.
I'm no expert. I just ...

I'd go for unscented lamp oil. Mix it with a heavier oil if that's what your valves need.
Valve oil and lamp oil are the same: it's all paraffine.

I can't remember playing a brass sousaphone which didn't ring. 24" bells ring less.
When playing with others I almost never notice it enough to be distracted. It comes with the gig, as it were.
When practicing I put two padded plastic spring clamps on the bell.
I never thought about using lead tape ...

Sorry, I couldn't resist and looked up the trailer.
At 0.45" you can see the Del Negro in action.
Sort of.

I think the real and only issue is;
Which one plays better?
Is more in tune?
Is easier to play?
Have less leakage at the valves?

One thing to keep in mind; a much older Conn (than 1946) is quite probably in high or low tuning.

With high tuning you can pull the slides to 440=A. If it still plays ...

Sorry
Humor’s not my forte.
Co- as in “joint” or “alongside”
An extra finger.
Oh well.

Charles Coffinger
Co-finger
That's it: Charles had six fingers!!!

Consider that downsizing might mean downgrading.
I moved from a 496 to a 497 because the instrument played better. Probably has to do with their being more handmade parts on the 497 plus a lot more attention to detail. It's a higher end tuba in all aspects. The better the tuba, the easier it is to ...

It's all a question of what you (think you) want.
I prefer to pull NO slides and have tuba's that come close to this requirement.
Fortunately I have work/gigs
Unfortunately way too many on sousaphone.

I have a fantastic 50's Martin medium with recently revised valves and awesomely lined slides ...

Makes playing 2p C & B a lot easier

I'm curious,
after all the work you put into it, why didn't you make the first valve slide tuneable with the left hand?