Yea, the output shaft seal and tail shaft, tailshaft, seal are the same thing. I didn't know what one was until mine disintegrated while removing drive shaft, to get the tranny out, to replace my clutch.
The seal probably costs only 5 or 10 bucks but the drive shaft has to come out and that means the gas tank comes down or the differential comes down, and that cost 100 bucks.
Getting the seal in / out of the tail shalft isn't that tough, but I also had my tranny out on the driveway when I pry'ed it out and delicately pounded it back in with a large piece of pipe.
It's sort of pinch, literally, to get the drive shaft out by just dropping the diff; there is just barely enough room. Like I said, I screwed mine up while doing just the same thing. I imagine the drive shaft comes out a lot easier by dropping the gas tank.
Think of it this way, if your biggest tranny problem is a leaky tail shalft seal then you are a blessed man indead. I would trade you in a minute!
Cheers
MB