72 915 input shaft seal
 

I have looked through many threads looking for the method of replacing the seal from the outside; w/o dissembly of the tranny

Ah yes, the wonderful engineering in regards to the 72. You got it right, that's pretty much the only way. I'm guessing it's leaking and spraying all over the clutch assembly? Some have drilled holes and created what is referred to as a dam, as is damn it this sucks.

Some reading.
http://forums.pelicanparts.com/porsche-911-technical-forum/196173-input-shaft-seal-problem-915-mag-case.html

If your 915 box is a 72 you can only do it from the inside and the whole box has to come apart!

Yes... did it a few times before going with the 'Dam seal' trick. The 72 trannys definitely suck!!

It is possible to have your transmission case "upgraded" to the newer style removable release bearing tube. There are a couple of places that offer that service.