What are the valve casings made of? My Sterling has stainless pistons with Nickel Silver valve casings, which when oxidized, can take on an orange color. As I continue to bring the horn back from sitting for years most likely, the valve oil turns kinda orange.
Hetman oils have some anti-corrosion bits in them, so if you can use them, I would stay with them. Broken valve guides though, that's just weird. They should be resistant to just about any type of solvent, and they shouldn't break down like that.
I will say that when a shop cleans a horn, they can use a lot of detergents and ultrasonic cleaners. this removes any type of oxide layer that is on the brass or nickel silver, which can make it more prone to flash oxidation.
Anyway, I hope you can get your valve issues sorted out. That's a great horn that deserves to be played!
Sterling / Perantucci 1065HGS Euphonium, 1952 B&H Imperial Eb Tuba, and a bunch of trombones.