The Celluloid scales that are on the Otto lends itself well to what is called an Acetone weld, (some people swear by this stuff called
MEK I haven't tried it) Just use a small wire and let a drop of Acetone wick into the crack... Hold it tight for about 1 minute then rinse with water...
The worst that can happen is you have to replace the scales anyway, the best that can happen is that the scales are fixed with a near invisible weld :) that actually holds pretty darn well...
Warning to others reading this Acetone/MEK welding doesn't actually work very often, there are many different formulas that were used to make scales and only some work... Most of the time people use to much and dissolve their scales :(