The Dark Crystal Promo Tape

I just came across a Preview Tape of The Dark Crystal in VHS format at
a local Good Will Store and I'm wondering if this is one of those
valuable finds.

The box has no DC artwork, just a blue case with the Buena Vista logo
on it.  Printed on the tape label are the words:

This cassette is the property of Buena Vista Home Video, and must be
returned upon request.

Does that mean that I technically have stolen Buena Vista property
since I have no intention of returning it?  Should I even take off the
wrapping (it's still sealed and wrapped)?

It also says:

NOT FOR SALE OR RENTAL

What if it IS worth some money?  Would I be bustin' rock in the pen if
I put this up on eBay?  Actually, this would probably be impossible to
sell there as they have some strict rules about these type of items.

Any comments?