I use Blue Juice. On the horns I play regularly, I put a few drops on each valve every couple days. For those that sit in their cases for weeks, quietly awaiting the thrill of being used, I oil before playing them, as Blue Juice evaporates fairly quickly. I've heard the tale of spitting on the valves to lube them in the days before valve oil. That would probably explain the worn-out valves on many vintage horns that were played very much.