99 western star 500 detroit 13speed $10000?

You can leak oil from the head or the "tappet cover" and it runs down.
I don't see the leak on the first picture but on the second it could be coming from the rear of the sump (oil pan).

 

Rear main is a cheap part , a head gasket set more but a fair amount of labor in changing either.
Also with a head leak there is a possibility of a more serious issue causing the leak.
Sometimes a head will seep a bit and a re-torque can fix that but if its leaking and running it is more serious.
The chances are slim that its the head.

 

After you run her 10,000 mi. it might go away,shes been siting a time now and all it needs is to get back on road !

 

You can get an oil additive that is supposed to soften and make old seals more supple.
It was meant for machines that had stood a while.
Don't know much about it.

 

Once you get the oil leak handled the only big thing extra I would worry about is checking the valve lash on your engine.

I recently bought a used truck and the first thing I did was take it in and had the valve lash checked and adjusted.
[Then I had the slack adjustors checked & adjusted; then I replaced a drivers door hinge.]

My truck is recommended to have the valves checked and adjusted every 250,000 miles; yours could be a different interval than mine though.

 

Did you go to a dealer with the sample or what? What was the turn around on results?