Your english is perfect!
If you could write your first posting again in english, it shall make more sense than the google translator.
Because the translator wrote, that you have a other (different) Transmission???
By the way: Use "Deepl Translate" much more professional!
For the Iltis-transmission it is not very common to make trouble with bad bearings.
Much more often there are leaking shaft seal rings.
If you talk about the 4th gear - it sounds more like a problem inside the gear-box part of the transmission.
But only 4th gear...over 60 km/h?
Have you tried 3rd gear with the same speed or more?
What happens, if you push the clutch as the noise appears?
Have you tried only in 2WD or also in 4WD?
If it is neccesary to switch the transmission, you have to remove the engine first - that is fact.
Very helpfull is the "VW-Iltis-CD" with all shop manuals:
http://forum.vw-183.de/index.php/topic,42545.0.htmlMaybe it could be helpfull for other users if you can upload an audio or video file with the noise?
And do you want to tell us your name?