Once again I dismantled the brake system on the rear axle. because I didn't trust this after market break shoes I bought earlier.
and once again i drained the dif-oil, and replaced it with a fresh quantity.
I also cleaned out the inner side of the dif with an low pressure solvent cleaner. (oh what a stink)and also checked the inner bearings. this was the point i noticed on the outside of the axel/dif an dust ring what was in an bit of an oval shape. when i turned the axle by hand, i heard the noise coming from this dust ring.
Replacing it solves the problem.
Well at least i know now for sure, that i have a well serviced rear Dana 35

Ready for the weekend, going again to the south of Germany (Bavaria) and Austria.
have a nice weekend you all