yes, there is a special tool but its not too special at all.
here's what you do.
remove the cover over the extension shaft.
find a long bolt bolt that threads in, (i knew the exact thread/pitch but i can't recal right now).
now get a long socket, a big washer like a large silver dollar sized, with the inner hole just big enough for bolt to fit thru. then a smaller washer, and a short socket.
Take the smaller washer put it thru the bolt. then the bolt and washer thru the smaller socket, place the larger washer thru the bolt/socket. now the long socket.
you should have bolt head>washer>socket>washer>socket>thread on the bolt.
now you want to thread the bolt in until the whole assembly is tight, the larger washer should be almost aligned with the trans housing (if the extension shaft is pulled in, it its out, then it'll be different).
now what you do with the special tool is use a pry bar on the larger washer to pull the extension shaft out from the diff, and gently push/hammer on the back of the bolt to push it back in.
remember to grease the extension shaft b4 pushing it back in.