Lennon window

Took this a couple of years ago as I was testing a Retina IIIc I had recently bought. Was very pleased with the results, unfortunately it seized up after about 8 rolls. I had a bit of a look inside with the thought to repair it myself if possible but didn't have all the necessary tools. It sat unused until recently when I gave it to my camera repair guy & asked him to look at it at his leisure.