[Bad Ass TA WS6]

Pretty common. The valve cover, actually has 2 gaskets. An inner (around the spark plug area) and an outer along the cylinder head.

200psi is too high (especially at 140K). I'd venture to say you didn't do a compression test in the proper manner.

Pull all plugs
thread your compression fitting into the SP hole, and attach your gauge
Turn the engine over 3-4 times, and record each cylinder.

The valve cover gasket leak isn't going to hurt your gas mileage.... You'll have a rough idle, due to faults in most cases. But even then, the area has to be SUBMERGED in oil to sometimes even get the car to misfire.

You've got other issues gauranteed.

For 1, at 140K, you're probably going to be looking at cataytic converters VERY soon. Do you have records of previous maintenance? How long have you had the car? When was the last Inspection II service done?