Oil leak on top of valve cover ?

There is an accumulation of motor oil atop the valve cover of this 2002 Chevy Trailblazer with an inline six cylinder engine. the oil is flung apparently and has been hitting the firewall and other sections of the underhood area. we went to auto zone and they sold us an oil sending unit which from what i can tell is located on the front passenger side of the engine block--nowhere near the leak in back.

Took it to my local area car garage and mechanic told .................
I think you have a bad gasket on your oil filler cap.

Replace it and the problem of oil leak is completely solved.