I’m a long-time fan of Hetman products. They have a wide range of oils and gels for just about every part of a brass (or woodwind) instrument.
I recently stumbled across this cool PDF that gives handy diagrams for where to best use their different products. I’ve mentioned some of the specific Hetman products I use on my French horn maintenance page, but this PDF could be a great reference to see the different options.
By far my favorite part of Hetman is the variety of oil or grease thicknesses. I use Hetman on horns (both 20+ years old), and having a heavier grease to use on the valve slides (which have gotten a little loose) really helps keep them in place. I use a lighter grease on the main tuning slides, so they are a bit easier to adjust.
Similarly, some of the ball linkages can get a bit noisy, and while a thick oil makes them quiet, it can also make them sluggish. Since all of Hetman’s oils can be mixed without any negative effects, you can even get “custom” viscosities. For my horn, I find applying bearing oil (#14) until the linkage is quiet and then adding some #13 one drop at a time until it moves quickly works best. While I have tried #13 (and #13.5) by themselves, they don’t seem to keep the linkage as quiet as long as the combination of #14 and #13.
If you’ve been having trouble getting your valves or slides to move “just right”, you should give Hetman products a try. They aren’t cheap, but they aren’t much more expensive than other oils, and they seem to both last longer and work better.
You can find the Hetman lubricants PDF here.
If you’re not sure exactly what to do for basic horn maintenance, you can find my French horn maintenance guide here.