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I used Hetmans Slide Gel and it makes all my slides SLOW (to slow....). Which ones do you use?

Vaseline. On clean slides it works really well. Plus it's really inexpensive (ie. a lifetime supply will cost you less than one bottle of Hetman's)

I agree with your assessment of the Hetman Slide Gel. It's too thick for tuba slides and doesn't 'bond' with the metal in a way that protects it from corroding and seizing up.

I resisted it for years because it's not 'cool', comes in an annoying bottle, and is 'gooey' BUT the Selmer pink slide grease really is pretty much perfect on any slide on any instrument. It makes slides easy to move when you want and keeps them in place when you don't. Works equally well on too tight slides and sloppy slides that need help to keep them from leaking.

Also, on slides that need to move a little faster, a few drops of valve oil thins it out nicely to customize the thickness to your needs.

It's also cheap. Just keep it in a ziplock bag in case the bottle cracks and leaks.

I second the STP oil treatment stuff, the selmer stuff is pretty good as well.
I have used the "guppy lube" stuff and it works well too. Basically, it's anhydrous lanolin with mineral oil mixed in.
I also have some Pro oils grease that's super thick...looks almost like marshmallow cream.

Anhydrous lanolin. Non-petroleum, easy to apply. Reasonably easy to remove. No smell. Not yucky and ultrasticky like STP (and did I say non-petroleum?). I think it is the primary ingredient in Schilke slide "grease" if you don't want to buy the pure lanolin.

Of course, if you're pulling a slide all the time, you'll need something thinner. For my first valve (vented) slide I use Alisyn. But any reasonable valve oil would work.