Head Gasket or Valve Cover Gasket Leak?

Anyone know what is causing this leak? Is this the head gasket or valve cover gasket? 2006 4.0L with 145K. No error codes / no engine issues thus far. This is the passenger side front of the engine.

I did notice my coolant is below the low line level in the overflow tank.

 

The dark staining appears to be a valve cover gasket leak(looks minor). The white spots might be from your overflow burping out some coolant. Check your oil if it's a head gasket it might be getting milky from coolant mixing in with it.

 

Always look at leaks from a "top-down" view. Your head gasket is below your valve cover gasket, so there's no way the leak could really travel upward and saturate your valve cover.

 

Unless its visibly pooling oil, I wouldnt worry about it, maybe stick a wrench on valve cover bolts to see if they are loose.

As far as coolant, it will naturally evaporate out of the overflow tank. Check n make sure (when cold) the radiator is topped off, and fill the overflow tank up and you will be golden.