above: where to apply lubricants to your rotors (source: Hetman's Lubricants catalog)
If you do not know how to take apart and reassemble rotors, please do not attempt to. There are many small parts that can be lost and other parts that can be bent or damaged. If you have never done this before, ask your private Tuba teacher or repair tech to show you how.
Rotors are relatively low maintenance...if they are cared for properly. Unlike pistons, which only require one variety of valve oil, proper rotor maintenance requires a few. The photo above is from the Hetman Lubricants Company. The numbers in the photo correspond to the following lubricants:
10: Musical Instrument Grease
11: Light Rotor - tight clearance (newer rotors)
12: Rotor - average clearance
13: Light Bearing
13.5: (I don't know, it isn't listed on Hetman's website)
14: Bearing and Linkage
The picture seems to display an excessive amount of oiling, but it isn't. Every part that moves or might experience friction should be oiled. The reason we use different oils is because different areas require oils of different viscosity, or thickness. We use a thinner oil on the face of the rotor than we do on the linkages because a heavy or medium viscosity oil on the rotor face would cause sluggish action.
You do not need to disassemble your rotors to oil them, but they should be disassembled and properly lubricated for bi-annual cleanings.
Here is what I use. I will correspond what I use to Hetman numbering above, so you know exactly where I oil.
11/12: T2 valve oil
Spindle and back bearing: Paxman bearing oil
10/13/13.5/14: Kraus medium weight oil
You can use alternatives, but I prefer to stick to lubricants made specifically for musical instruments. Some alternatives I have seen used are 5W-30 motor oil, 3n1 oil and STP oil additive. When used in the proper areas, they work fine, but I prefer to use products made for musical instruments specifically.
Here is another useful illustration from the Yamaha Company:
If you keep your rotors and linkage properly oiled, it will keep your horn quiet and happy for many years to come. Here are a few useful links: