Thanks guys, and especially Shooter. A Linear wipe did the trick nicely. It is not 100% because the wipe obviously reveals the film strip, as opposed to the film's leader travelling across the screen, but this takes place over just 12 frames so I doubt anyone is going to notice.
I would have done it like this.
Duplicate (alt-drag) the clip of the Cannister and place it on a video layer 2 above the original clip
Apply a linear wipe * to the top one set to the edge of the cannister.
Between the two layers I would have had the film strip ( which I presume is an element ie. a clean object)
Animate the filmstrip using Motion, Poition ( keyframes)
* The linear wipe tweaked for edge and angle