Seems to me then that the case was milled properly, but the retaining ring is now too wide. My guess is that a gen 116 will not be wide enuff either. The ring was either made incorrectly and/or was deformed by pressing it in a crystal that was to wide, there by permanently widening the ring(it's happened to me before on a gen 5513 ring).
So, a cheap solution might be try an aftermarket 127. It should fit the case, but will be a bit tall. Hence, you could sand it down on a flat table with 600, until it's the same height as the 116. It should be slightly wider and hopefull fit snug with your current retaining ring. I'm fairly certain the 127 is a touch wider than the 116.
Worth a try and experimenting with a $10 crystal is cheaper than getting a new ring custom made. Just a thought.