Beseler Negatrans for the 23c. Will also fit the Beseler 45. Shows wear but working. The o-ring is intact and working, but has cracks, so plan to replace sooner or later (replacement available on ebay for about $10). $25 plus actual shipping.
Yes, they are. This one is an extra; I have one that I use on a 45 and a 23c.
In case you're not familiar with these, they allow you to insert a strip of 35mm film (or a whole roll I suppose) and, by turning a wheel, cycle through each frame for printing.