I've located a bit of 16mm film - about 3mins all told - which features some behind-the-scenes shots from Dark Crystal, Empire Strikes Back and Return of the Jedi, intercut with clips from the finished films (plus a bit of The Great Muppet Caper for some reason) and a brief clip of Jim Henson talking.

It's been suggested that this may be an excerpt from Classic Creatures: Return of the Jedi, but not having seen this I can't confirm.  Does the above sound at all familiar to anyone?  If it's taken from a documentary then it's probably of little interest, but if it's unique then I shall see about getting it put onto video.

Thanks!