Do this on a monthly basis, and make sure all dirt is removed before applying the oil. Use a needle oiler, and take care that no oil comes into contact with the plastic body of a pupil instrument. Check to see that the screws are in place and have not twisted themselves out of the post. Lost screws will mean lost keys. If the screw is too far out, tighten it with a small screwdriver until it is level with the post, but do not overwind the screw, as the key may bind. If in doubt, hunt down a certified repair person to fix, hold and adjust screw tensions. Wooden clarinets are sometimes subject to cracking, a condition we all hope to bypass. Cracking can occur if a part of the wood absorbs moisture and expands while other sections are too dry; the change in pressure can cause a crack. The same can be said of temperature. If you blow hot air through a cold tool, the temperature change may cause the bore to expand while the outside is still cold and shrunk. Either way, the force on the wood is inconsistent, and cracking is possible.