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I've been working on (two or three left to go - hopefully, I'm past the worst) roughly a dozen (not only professional and close-to-professional grade trombones, but also) silver plated and F-attachment instruments for a school. These are all taken outdoors, and several of their slides were "creamed".

It should go without saying that I can - fairly quickly/easily - fix all the junk wrong with their bell sections (including realignment main tuning slides - after un-smashing their bows, straightening out bells, replacing missing thumb linkage parts, etc.), but - regarding the playing slides - since the tubes are silver plated, they're all going right back out to do more outdoor war, these instruments are made in the USA, the manufacturer - these days, supplying parts - is as slow as molasses (going to remain in business...??), I've been entertaining myself repairing playing slide tubes that - under normal circumstances - I would be throwing in the trash (particularly if repairing for pros), and - actually - these slides are turning out so very "good enough" that some of them are actually prompting me (upon completion) to giggle, just a little bit.

I'm employing some crazy techniques (and some of my techniques aren't used by very many - if any - others anyway) that have never occurred to me before to try, and several of them are proving to be 95%-or-better successful. One thing - that I tried...and it worked, employed using a vice (and not just to support a repair tool).

Well, I suppose if you use the vice to make the diameter small enough that it doesn't scrape when in use, that's good enough for kids to use outdoors.

I'm having to hurry through this stuff, so I didn't have time to experiment to see how close to perfectly round I could get a damaged area of a slide tube, but I managed to get an area - that was horribly oval - down to the point that it only varied about .003" as I ran the calipers around the tube, and that's just from squeezing it crudely with a no-teeth vise, but trying to be a good guesser.

That sounds like something I would resort to if I just HAD to get a slide to work. Hilarious really -- you should disguise yourself and make a youtube video. The screeching would be off the scale.
I have a bass tbone that I sold and rebought later (sound familiar?) and it came back with a slightly crunchy slide past about 4th position. But I don't think I'll put it in a vice. I can't hold it up and would rather re-sell it, but with the 7 out of 10 slide, it would have to go cheap.

When I'm repairing really messed up slides, I either take them completely apart - to isolate the four tubes, or I'll at least take off one tube and isolate it. I put them on a very slow-turning lathe, so I can see where they're a bent, and if they happen to be out of round/ovalled, the lathe shows that up very clearly as well. I wasn't guessing as to where it was oval, but I was guessing whether the crazy technique to make it round again would work. Human fingers - at least mine, which I consider strong - aren't strong enough to squeeze chrome-plated nickel-silver inside slide tubes back round again, but a vice seems to be strong enough.

I read where a lot of people place playing slide tubes against really straight flat surfaces and look at the light and blah blah blah... maybe that's completely revealing to them, but - to me - there's nothing that shows up flaws in playing slide tubes more than just sticking them on a lathe and letting them spin slowly. Fortunately, most of them are only crooked and not ovaled. I find the centers of the wobbles, mark them with a sharpie or a crayon, release tension on the tube from the lathe, address the wobble, spin the tube again, and determine whether I've done just enough, not done enough, or done a bit too much. I quit working on them when they look like they're sitting still while they are spinning. Prior to mounting them on the lathe and straightening them, I remove any dents that might be in them. This requires some experience, because it's really easy to bulge or oval a playing slide tube when removing dents from them. Bad bulges behave in the same way that oval places behave, except there's no hope in fixing a bad bulge.