So for search purposes in the future, we called up IWE, who told us to go to Bert's Automatic Transmission on Kingsway in vancouver. Some money and 3 hours later the diff is back together and the c-clip is magically in the godd*mn slot.
Pretty good place imo. Dude recognized the diff as a "nissan Rxxx" diff right away. Pretty good for just seeing the casing.