That rear output shaft seal is a bad seal to leak I think.
I assume the x-drive rear output flange is like the non x-drive TCase flange…held on with a big nut. If so, I did a full rebuild on an eBay TCase last year and swapped it into my e53. I did the chain and all the bearings and seals (and front output shaft), except for that rear output shaft seal and bearing. Fortunately that bearing was fine. I was concerned that I wouldn’t have a way to re-torque the big nut holding that output shaft flange on. Or even hold it while it is being re-torqued.
I bet you could zip it off with an impact pretty easily, but the ring gear may need to be removed as it drives the output shaft. I wasn’t sure what was involved in getting that out. Would it just all come apart when the nut was removed…hopefully. On the other hand, if you can get the output flange (5) and dust shield off, you may be able to get the seal out by drilling a hole in it to pry on. Then you can drive a new one in with a deep well socket.
The other seals and bearings on the non x-drive TCase were easy though. You may want to consider the route I took. Get an eBay t-case and rebuild that one, then swap it in. With any luck that seal and bearing will be ok, and you can take your time on the chain, etc.