Excalibur is a commercial sheath cleaner that has been around for a long time. It is a detergent with a solvent in it that breaks down fatty sheath secretions. It also apparently contains Tea Tree oil which is purported to have antiseptic qualities. I have always used ivory or Palmolive soap, which is mild and has some grease dissolving qualities.

Whatever product you use, be sure it is not antiseptic or harsh in any way. Products should be used that do not disturb the natural bacterial flora of the sheath. Always rinse out the agent from the sheath as well as possible.