Had new gears installed, just checked for leaks, all is good on the diff's but noticed fresh leak of trans fluid where front of the drive draft goes into slip yoke. It is coming from the rubber seal that goes around the front of the drive shaft. I thought there was only grease in there ? Is there a seal under/in the slip yoke to the trans or - dumb question - could the gear shop have used trans fluid as a lube ??

 

Replaced rubber boot that front of drive shaft slides into. All is good.

 

I have this same problem, a leaking tcase at the output shaft. That rubber flange should not be the problem as I've replaced my entire rear housing of the tcase (which just looks like a cone). I also replaced a rubber o-ring seal inside of that cone. Still leaks like a *****.