Diff oil in tranny, how to fix?

[RalphM]

AV8 has been getting overfull tranny, diff is low. It's a 37 tranny and rear axle, but I shortened the tube, took out the center bearing and put in a 34 style hollow driveshaft. Now it's got a little bit of rake, so I'm assuming this is allowing fluid to move forward. Does anyone make a seal that I can put back by the diff to keep the oil in it?