Last night, after I parked at Wal-Mart, I discovered that in the front right wheel case there is a large black spot all around. I checked and found that this must be from a leak and this needs to be fixed. I checked online and found two potential truck shops. Early in the morning I called them both and the second one (Womack Diesel) accepted me right away.
This looks like a family business and they took care of it right away and found, that there was a leak. This thing is leaking pretty good, he said and within an hour or so they started working on it. Taking everything apart, they found that the seal was just worn out pretty good and a replacement was at hand.
Within a few hours I will be on the way again.
Here are some photos.