Hello everyone. I'd like to share some good news. I was able to retrieve the washer, but not without the help of a friend who managed to secure a loaner on a medical endoscope. The fiber optic light source is great for lighting the recesses of the case and the scope allowed to me to confirm the location of the washer and get it out with a creatively bent magnet. The fiber is so thin, you can slip it between the aluminum gear and the case (< 1mm). Close call for me and a lesson learned. Thanks everyone for your suggestions and sympathy and I hope this thread can help another unlucky engine builder in the future.
