I quizzed my wife on the sound, she said it was a very loud clanging noise, which makes me think that something may have let go internally. Might be a crack in the case or rear cover causing the leak. I've never seen anything like this.

I have been able to find out that the diff is specific to the model, 2.65:1 ratio. There's some difference related to anti-lock brakes, I'm not sure what it is.The 190 16V had a 3.27 rear, which would be "good enuf", if I could find one, and be sure of fit.