The wheel is concave. It rides on the track. These are the parts. The metal cylinder broke.
I wrote measurements down. Hope you can flip the image. If you don't make it, or a reasonable replacement, can you recommend someone who does?
Paul from SWISCO responded:
May 1, 2014
We may be able to help, yes. Look at our 87-006 and 87-006A and see if either of these could work for you as a replacement.