Generally speaking, collectible knives and their leather sheaths should be stored separately.
Whatever you put on the blades to protect them may be harmful to the leather.
The chemicals used to tan the leather may stain the blade.
All-in-all, it's best to keep them separate. Some people will cut and form a piece of wood or plastic into the shape of the blade and put that into the sheath to keep the shape.
Keep in mind that your knife is a cutting, stabbing tool (even a Hibben (sorry, I'm trying to contain myself)) and it can cut or stab the sheath as you take the knife in and out. So, it's often best not to risk damaging the sheath.
There've been some really good threads here in the past about care and storeage including some frightening threads about mistakes people have made that have ruined valuable knives. So, I'd suggest some time searching the archives.
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Chuck
Balisongs -- because it don't mean a thing if it ain't got that swing!
http://www.4cs.net/~gollnick