This is my first Mini: 2010 non-"S" Clubman. The shop I use for maintenance is telling me my pressure is too high, (spec is 8, and I'm at 13) and the breather valve is the culprit and is part of the valve cover. They are telling me it's a $500.00 fix.

Any knowledge concerning this would be graciously appreciated.

"Keep the rubber down"

 

They are correct.
The internal crankcase ventilation system is integrated into the plastic cylinder head (valve) cover. The crankcase breather valve is part of the cylinder head (valve) cover and is NOT serviceable as a separate component. ...The pressure control valve varies the vacuum applied to the crankcase breather depending on engine load. The valve is balanced between spring pressure and the amount of manifold vacuum..."