Bxx1 Buying a dye leak kit would be the first thing. Put the car up on jack stands and run it through the gears a couple of times. It could be coming from the top cover plates, speedo gear housing hole, rear extension housing gasket or yoke seal.
Since you blew up 2nd gear, I am going with a possibility of hard driving or too much power for this trans. If you are 100% sure the
oil is coming from the rear yoke area, see how much play you have when you push up and down on the drive shaft in neutral. There should be maybe 1/8" total any thing more and the bushing is worn out in the tail housing. Is it possible that the case is overfilled and blowing out the vent hose or tube?
The other thing would be to mic the yoke and check for the correct outter tube spec. It could be worn. The bushing is designed to wear out and not the yoke. Some yokes are not made of the right materials. The seal even beening rubber also could wear out a groove in the yoke and also cause a leak.
Down the road if you keep the car you might want to look at a better trans like a TKO 500 or better a 600, and should n't have to worry about breaking 2nd gear again. If you add the repair bill up 2-3 times you have enough for the new trans. See Bylins for a price, he's cheaper than Summit or Jeg's and stand behind what he sells. Rick L.